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00:00:06,280 --> 00:00:09,000
There are still parts of
our planet...

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..yet to be explored.

3
00:00:17,640 --> 00:00:19,880
Descending!

4
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These are remote
and unforgiving places...

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I'm in.

6
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..and the journey to reach them...

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We're in very real danger of
getting trapped here.

8
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..will push me
and a team of explorers...

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Ugh. Ugh, ugh.

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..to the limit.

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00:00:36,160 --> 00:00:38,320
STEVE SHOUTS

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It looks like he's coming back.

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The reward...

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Amazing!

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..breathtaking new discoveries.

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When you're standing in a place
that no-one has ever stood before,

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it's very, very precious.

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This time we're in the
Yucatan Peninsula of Mexico.

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Check that out.

20
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We want to explore
a vast, flooded cave system...

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Are you ready?
Happy as I'll ever be.

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..deep beneath the jungle floor...

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Absolutely no idea what's up there
in the darkness.

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..to find and map new passageways...

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This is absolutely magical.

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..but this is one of the most
dangerous environments

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on the planet.

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It's just essential that
nothing goes wrong now.

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Oh, it's zero visibility.

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I don't know where I'm going.

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It just blows your mind
that somewhere like this

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can still exist in the 21st century.

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This is what adventure is all about.

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Beneath this jungle is the largest
network of unexplored caves

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in the world.

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The way into them is through
openings called cenotes.

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What we want to try and find
is a new cenote

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that's not been visited,
and that's never been explored.

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Our mission is to find one
that leads to a network

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of new connecting passageways.

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The Yucatan has thousands
of cenotes.

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Near the coast, many are tourist
attractions,

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but head inland, and it's
estimated that as few as 1%

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have been discovered,
let alone explored.

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And the exciting thing is,

46
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this expedition could be the first
to take light

47
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into cave systems that haven't
been illuminated EVER.

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The Peninsula is composed
of limestone,

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eroded by movement of rainwater

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and constantly changing sea levels
over millions of years.

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Now, it's a honeycomb of
subterranean caverns.

52
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Sometimes a void is so big

53
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it can't support the weight
of its own ceiling,

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which will collapse, leaving a hole
in the jungle floor...

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..and it was the Maya,

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the ancient civilisation that
dominated this part of the world

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2,000 years ago,
that named them cenotes.

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They believed them to be a portal
into an underworld called Xibalba,

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the place of fear.

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Many who tried to enter this world
never came back.

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Modern diving technology
means it's now possible

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to explore this underworld,

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but it's definitely not
without its dangers.

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If you run out of light or air

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and you're even a couple of
hundred metres below the surface,

66
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you're not coming up again.

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You know, I've done several thousand
dives,

68
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but I've done fewer than 100
in caves.

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That's not a lot.

70
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So this is well out of my league,

71
00:05:05,080 --> 00:05:07,680
and I guess we're about to
find out if it's...

72
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..if I'm properly out of
my depth.

73
00:05:11,560 --> 00:05:14,560
I did my first cave dive years ago,

74
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but have spent the last few months
in intensive training.

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Unlike ocean scuba diving,

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where I would normally carry
a single rear-mounted cylinder,

77
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in a cave, we'll carry two mounted
on the side,

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which will give us more breathing
gas and a backup if one fails.

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With cylinders in this position,

80
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we'll be able to squeeze more easily
through narrow spaces,

81
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but the deeper we push,

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the further we'll be from the safety
of the surface and natural light.

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We need to unfurl lifelines
as we go,

84
00:06:02,240 --> 00:06:04,960
which show us the way back out
if our torches fail.

85
00:06:09,680 --> 00:06:12,680
You ignore these rules
at your peril.

86
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There are rarely injuries
in cave diving.

87
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You either live...or you die.

88
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I'm in the coastal town of Tulum,
my base for the next month,

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and with stakes as high
as they are,

90
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I've brought in a crack team of
cave divers to help me.

91
00:06:47,920 --> 00:06:52,480
Robbie Schmittner is arguably
the world's top underwater cave
explorer,

92
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and a personal hero.

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Joining us is underwater
camera operator Katy Fraser...

94
00:07:01,680 --> 00:07:03,960
That's very light -
that's going to fly.

95
00:07:03,960 --> 00:07:06,320
..dive supervisor Scott Carnahan...

96
00:07:06,320 --> 00:07:08,520
Who is it?

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..and with over 20 years of
cave diving experience,

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00:07:11,840 --> 00:07:14,800
Mexican instructor
Bernadette Carrion.

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With only a few days before
we begin our exploration,

100
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we're heading 7km west of Tulum
for more training.

101
00:07:29,880 --> 00:07:32,920
Around here are many cenotes
that have already been explored.

102
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They're the perfect place to
fine-tune my cave diving skills.

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Let's go do it.

104
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With Bernadette's help,

105
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I need to ready myself
for the challenge ahead.

106
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Scott? Yes, sir?

107
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Are we on nitrox?

108
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Yes, you are, 30%.

109
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Bernadette, can you just check
I've got this the right way round?

110
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Now you need to get it
on the other tank.

111
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So, diving is already

112
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one of most logistically challenging
things we do.

113
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Cave diving is a big step up
from that,

114
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but that's not difficult
enough for us.

115
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We're going to try
and film it as well.

116
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So that just makes it...

117
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Well, you can see all the kit
lying around everywhere.

118
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And, you know, what could possibly
go wrong?

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Everything could go wrong.

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STEVE LAUGHS

121
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I know all the basics now.

122
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In this training dive,

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I need to bring everything
together,

124
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to move at one with my equipment,
confidently.

125
00:08:44,200 --> 00:08:45,960
It just doesn't feel right, Scott.

126
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Is that supposed to be like that?

127
00:08:51,680 --> 00:08:54,800
Looks like the torch has
just come on, Steve.

128
00:08:57,240 --> 00:09:00,880
Just feels like an awful long
stretch.

129
00:09:06,800 --> 00:09:10,160
I'm really struggling
with this today.

130
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I'm much more familiar with gear
that's set up for ocean diving.

131
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This rig is a whole different story.

132
00:09:18,960 --> 00:09:20,960
HE SIGHS

133
00:09:24,560 --> 00:09:29,120
We rely completely on our
equipment in cave diving.

134
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That's why we carry everything
double and triple.

135
00:09:32,600 --> 00:09:38,480
Three lights, two regulators each,
and that is why...

136
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..because we can not go up to
the surface.

137
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We're under the ceiling
and sometimes

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we are 800 metres to a kilometre in
the cave,

139
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so we need to fix problems there
and make sure we can get back out.

140
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Anything goes wrong,
and you're on your own.

141
00:09:54,080 --> 00:09:55,880
Exactly.

142
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There is a saying in cave diving -

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slow is smooth and smooth is fast.

144
00:10:00,800 --> 00:10:03,240
So keep it slow, keep it nice,
keep your train,

145
00:10:03,240 --> 00:10:05,720
keep your buoyancy and, erm...

146
00:10:05,720 --> 00:10:07,480
..that should bring
everything else

147
00:10:07,480 --> 00:10:10,480
from what you learned on your
training into position.

148
00:10:10,480 --> 00:10:11,480
OK.

149
00:10:42,400 --> 00:10:46,080
It's a really spooky sensation...

150
00:10:46,080 --> 00:10:48,640
..heading into the darkness.

151
00:10:48,640 --> 00:10:52,200
Kind of every part of your body
is screaming out at you...

152
00:10:52,200 --> 00:10:54,400
..that it's a crazy thing to do.

153
00:10:56,680 --> 00:11:00,720
The water in a cenote is filtered
as it passes through the limestone.

154
00:11:02,040 --> 00:11:06,400
The water is so clear,
it almost feels like you're flying.

155
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The big danger is that you lose
that visibility

156
00:11:14,480 --> 00:11:18,200
and everything goes cloudy
and you don't know where you are,

157
00:11:18,200 --> 00:11:21,680
and that can happen from kicking up
silt from the bottom...

158
00:11:23,280 --> 00:11:25,800
..or even just from your bubbles.

159
00:11:29,600 --> 00:11:33,120
So when my bubbles go up to
the ceiling,

160
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it starts to bring down
all this sediment.

161
00:11:36,280 --> 00:11:38,720
You have to be very, very careful.

162
00:11:51,320 --> 00:11:54,640
I'm throwing up a much bigger
silt cloud than I was expecting.

163
00:11:56,960 --> 00:11:58,840
Fortunately this cave
is already mapped,

164
00:11:58,840 --> 00:12:01,240
and there are pre-laid lifelines
to follow...

165
00:12:04,920 --> 00:12:08,240
..but when we explore new caves,
we'll lay our own.

166
00:12:08,240 --> 00:12:11,000
If things go wrong,
our lives will depend on them.

167
00:12:20,880 --> 00:12:24,800
I'm keen to know what Bernadette
made of my dive.

168
00:12:27,440 --> 00:12:31,440
You really seem very calm
and relaxed down there.

169
00:12:31,440 --> 00:12:33,520
Your position, it looks good.

170
00:12:33,520 --> 00:12:36,600
You don't look like
as if you're going to die -

171
00:12:36,600 --> 00:12:38,200
at least, I think.

172
00:12:40,680 --> 00:12:43,360
Bernadette's confidence
in me is good to hear...

173
00:12:46,160 --> 00:12:48,960
..but there's still
a lot of work to do.

174
00:12:55,280 --> 00:12:57,680
As the expedition phase gets closer,

175
00:12:57,680 --> 00:13:00,960
I'm spending as many hours as I can
in the pre-mapped caves,

176
00:13:00,960 --> 00:13:02,760
honing my skills.

177
00:13:05,440 --> 00:13:08,160
Where we're headed, off the map,

178
00:13:08,160 --> 00:13:11,960
the passageways may barely
be wider than I am.

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00:13:11,960 --> 00:13:14,280
My technique will need to
be flawless.

180
00:13:20,880 --> 00:13:24,320
But by far the biggest challenge
is my own mind.

181
00:13:29,160 --> 00:13:31,120
I need to suppress panic...

182
00:13:32,680 --> 00:13:33,680
..keep calm...

183
00:13:35,520 --> 00:13:38,280
..and expect the unexpected.

184
00:13:49,920 --> 00:13:51,480
There's a crocodile!

185
00:13:53,600 --> 00:13:59,080
Cenotes are very occasionally
a sanctuary for young crocodiles.

186
00:13:59,080 --> 00:14:02,520
I'm going to approach
quite cautiously,

187
00:14:02,520 --> 00:14:04,040
cos I don't want to spook him.

188
00:14:09,920 --> 00:14:12,630
Whoa! Amazing.

189
00:14:12,630 --> 00:14:15,950
Swimming straight at Robbie's head!

190
00:14:15,950 --> 00:14:18,270
Well done getting
out the way of that, mate.

191
00:14:24,230 --> 00:14:26,110
Taking a break from training,

192
00:14:26,110 --> 00:14:28,350
I use the opportunity to
look for an animal

193
00:14:28,350 --> 00:14:31,950
that was once important to
the ancient Maya.

194
00:14:33,430 --> 00:14:38,950
WILDLIFE SCREECHING

195
00:14:38,950 --> 00:14:40,350
It's a great sound.

196
00:14:40,350 --> 00:14:43,110
That is the voice of the cenote.

197
00:14:43,110 --> 00:14:48,190
BIRDSONG

198
00:14:48,190 --> 00:14:50,310
These are motmots.

199
00:14:50,310 --> 00:14:53,670
Once we get off in the forest
and it's all featureless,

200
00:14:53,670 --> 00:14:55,550
we'll be listening for that sound,

201
00:14:55,550 --> 00:14:59,150
cos that will tell us
there's water nearby.

202
00:14:59,150 --> 00:15:01,830
Motmots are only ever found
near water,

203
00:15:01,830 --> 00:15:05,310
and they only nest in limestone,

204
00:15:05,310 --> 00:15:09,510
so if you hear them in the jungle,
you must be near a cenote.

205
00:15:09,510 --> 00:15:12,790
It's not surprising the motmots
were very special birds

206
00:15:12,790 --> 00:15:14,750
to the ancient Maya.

207
00:15:14,750 --> 00:15:17,070
It's like they're a guardian
to the underworld.

208
00:15:21,670 --> 00:15:24,590
I'm down to my last few hours
of training with Bernadette

209
00:15:24,590 --> 00:15:26,990
before I head off the map
with the rest of the team.

210
00:15:29,670 --> 00:15:33,550
Today she's testing me in a cave
well known for disorientating

211
00:15:33,550 --> 00:15:35,750
even the most experienced divers.

212
00:15:50,350 --> 00:15:53,830
It's like a river,
flowing underneath the water!

213
00:15:56,230 --> 00:15:58,430
My mind just can't take it in.

214
00:16:05,230 --> 00:16:07,270
This is a halocline.

215
00:16:09,070 --> 00:16:11,710
They can only occur here,
near the coast,

216
00:16:11,710 --> 00:16:14,230
where a dense layer
of salty sea water

217
00:16:14,230 --> 00:16:16,950
meets a lighter layer of
fresh water.

218
00:16:20,630 --> 00:16:22,990
It's completely disorientating.

219
00:16:24,470 --> 00:16:26,990
I can't tell where I am.

220
00:16:32,870 --> 00:16:35,910
It's incredible,
but I mustn't forget

221
00:16:35,910 --> 00:16:38,910
this is a potentially dangerous
underwater cave.

222
00:16:41,590 --> 00:16:43,710
As I complete my training,

223
00:16:43,710 --> 00:16:45,990
I'm constantly reminding
myself to be wary...

224
00:16:51,550 --> 00:16:54,310
..but I think the risks
are worth taking.

225
00:16:54,310 --> 00:16:58,430
Our expedition is more than just
exploration for the sake of it.

226
00:17:02,510 --> 00:17:06,150
These cenotes are the only
natural source of fresh water

227
00:17:06,150 --> 00:17:09,710
for human and animal life
across the whole Yucatan.

228
00:17:11,230 --> 00:17:15,830
It's a precious resource,
but it's under threat.

229
00:17:15,830 --> 00:17:16,910
Look at that!

230
00:17:18,470 --> 00:17:21,110
After last night's rains,

231
00:17:21,110 --> 00:17:25,470
there's a slick running down
the surface of the water -

232
00:17:25,470 --> 00:17:27,910
oil and other pollutants.

233
00:17:27,910 --> 00:17:31,750
It's easy to see how
the entire water system here

234
00:17:31,750 --> 00:17:35,950
can be contaminated
from our waste on the land.

235
00:17:40,270 --> 00:17:41,750
The coast of the Yucatan

236
00:17:41,750 --> 00:17:44,870
is the fastest growing tourist
hot spot in the world.

237
00:17:48,190 --> 00:17:52,070
People come here in their millions
to stay in luxury hotels

238
00:17:52,070 --> 00:17:55,630
that are sited right on top of
the underground cave systems.

239
00:17:58,710 --> 00:18:01,990
Scientists are concerned
that chemicals in waste water

240
00:18:01,990 --> 00:18:04,710
from the town of Tulum
are leaking underground

241
00:18:04,710 --> 00:18:08,110
and finding their way into caves
many kilometres away.

242
00:18:11,950 --> 00:18:16,350
With tourist numbers set to
increase tenfold by 2030,

243
00:18:16,350 --> 00:18:19,750
the whole of Yucatan's
underground water network

244
00:18:19,750 --> 00:18:22,070
is at risk of being contaminated.

245
00:18:24,550 --> 00:18:28,030
So how many of these cenotes
have you tested, Arturo?

246
00:18:28,030 --> 00:18:31,590
Well, we have more or less 50.

247
00:18:31,590 --> 00:18:35,870
As more cenotes are monitored
in and around the Tulum area,

248
00:18:35,870 --> 00:18:39,190
more evidence of human contamination
is being found.

249
00:18:39,190 --> 00:18:40,590
How much do you need, Arturo?

250
00:18:40,590 --> 00:18:42,950
Maybe full, please.

251
00:18:42,950 --> 00:18:48,550
Water testing is just one step
towards understanding the problem -

252
00:18:48,550 --> 00:18:51,150
another is to appreciate
how widespread

253
00:18:51,150 --> 00:18:53,230
and interconnected the caves are.

254
00:18:55,030 --> 00:18:58,830
For that, we need to
explore and map.

255
00:19:03,150 --> 00:19:07,030
Robbie knows of one particular cave
that's ripe for exploration.

256
00:19:07,030 --> 00:19:11,270
It could be the way into
a new network of passageways.

257
00:19:20,630 --> 00:19:23,910
We're looking for a clearing
to land our heavy diving kit.

258
00:19:26,070 --> 00:19:29,230
We're right over it. I can't see it.
We're right over it, yeah.

259
00:19:30,470 --> 00:19:32,390
But even with GPS coordinates,

260
00:19:32,390 --> 00:19:35,230
we're struggling to spot
the cenote itself.

261
00:19:36,430 --> 00:19:38,270
It's a lot of jungle.

262
00:19:38,270 --> 00:19:41,430
The terrain is just a nightmare.

263
00:19:44,590 --> 00:19:47,630
Robbie is at the vanguard of
a scientific project

264
00:19:47,630 --> 00:19:49,430
which is charting the cave system.

265
00:19:52,150 --> 00:19:55,870
He has single-handedly mapped 900km

266
00:19:55,870 --> 00:20:00,030
of the 1,400km that are known,

267
00:20:00,030 --> 00:20:03,470
but thinks he has only
scratched the surface.

268
00:20:17,110 --> 00:20:18,750
Only by mapping the caves

269
00:20:18,750 --> 00:20:23,030
can we understand how water
moves through them.

270
00:20:23,030 --> 00:20:25,230
Then, together with water testing,

271
00:20:25,230 --> 00:20:27,910
we'll know how far pollution
is spreading

272
00:20:27,910 --> 00:20:31,150
and hopefully where
it's coming from.

273
00:20:31,150 --> 00:20:33,350
Every metre Robbie maps for them

274
00:20:33,350 --> 00:20:35,790
adds to the scientists'
understanding

275
00:20:35,790 --> 00:20:37,750
of this fragile life support system.

276
00:20:40,470 --> 00:20:43,510
But of the thousands of cenotes
out here,

277
00:20:43,510 --> 00:20:46,110
this one in particular
has eluded him.

278
00:20:48,350 --> 00:20:50,390
Known as Satelite,

279
00:20:50,390 --> 00:20:53,030
he first heard rumours of it
20 years ago.

280
00:20:55,110 --> 00:21:01,750
In 2017, he led a group in search of
it and they found the entrance.

281
00:21:11,150 --> 00:21:14,390
From up here, it's obvious
that the jungle is too thick

282
00:21:14,390 --> 00:21:16,950
to land our gear by helicopter.

283
00:21:16,950 --> 00:21:20,670
We're going to have to get it all
out here on foot.

284
00:21:20,670 --> 00:21:22,710
THUNDER RUMBLES

285
00:21:25,150 --> 00:21:28,430
So, logistically, Scott,
what are we looking at here,

286
00:21:28,430 --> 00:21:33,590
if we're talking about getting 8km
inland through the forest?

287
00:21:33,590 --> 00:21:36,270
Well, I think, realistically,
we definitely can't

288
00:21:36,270 --> 00:21:38,150
carry everything in one go.

289
00:21:38,150 --> 00:21:40,790
I mean, there's not enough of us
to carry all the tanks,

290
00:21:40,790 --> 00:21:44,630
so we need to get in there,
set up a base camp

291
00:21:44,630 --> 00:21:47,670
and see if it's worth carrying
the rest of the stuff out.

292
00:21:47,670 --> 00:21:49,470
So how are you feeling about this,
Katy?

293
00:21:49,470 --> 00:21:52,510
I mean, obviously cave diving
and filming in caves

294
00:21:52,510 --> 00:21:54,390
is your thing and is your job.

295
00:21:54,390 --> 00:21:59,270
From a filming point of view, these
caves are so aesthetically beautiful

296
00:21:59,270 --> 00:22:02,070
that it is really hard
to get a bad shot,

297
00:22:02,070 --> 00:22:05,230
and that's why I fell in love
with them.

298
00:22:05,230 --> 00:22:08,190
And to come across these places
for the first time and capture it,

299
00:22:08,190 --> 00:22:11,790
and capture everybody's emotions,
and have it on film,

300
00:22:11,790 --> 00:22:14,510
will be really, really
special for me.

301
00:22:14,510 --> 00:22:18,110
All we need now is just
a symbol from the rain gods.

302
00:22:19,590 --> 00:22:21,590
THUNDER RUMBLES

303
00:22:21,590 --> 00:22:24,750
There we go.
There you go - the gods say "yes".

304
00:22:24,750 --> 00:22:25,830
Or "no".

305
00:22:25,830 --> 00:22:27,790
Doesn't feel like "no" to me!

306
00:22:30,630 --> 00:22:33,950
Satelite awaits us, far off
in the dense jungle...

307
00:22:36,830 --> 00:22:38,870
..but our point of departure

308
00:22:38,870 --> 00:22:42,030
highlights the uglier side
of urban life.

309
00:22:47,550 --> 00:22:52,270
This is certainly the weirdest start
to an expedition I've ever had.

310
00:22:52,270 --> 00:22:55,710
It turns out that the best way
for us to get into the forest

311
00:22:55,710 --> 00:22:58,470
is through the town dump.

312
00:22:58,470 --> 00:23:01,230
It's kind of a vision of hell,

313
00:23:01,230 --> 00:23:05,670
but, you know, everywhere has to
get rid of their rubbish somehow.

314
00:23:07,550 --> 00:23:10,950
But here outside of Tulum
in the Yucatan,

315
00:23:10,950 --> 00:23:15,030
because of what we know about
the geology here,

316
00:23:15,030 --> 00:23:18,670
it's kind of got much more impact.

317
00:23:18,670 --> 00:23:22,790
Loads of pollutants are going down
into the cave systems,

318
00:23:22,790 --> 00:23:26,630
and the fresh water that's flowing
through them is the same fresh water

319
00:23:26,630 --> 00:23:30,430
that the people here,
and the animals, completely rely on.

320
00:23:33,830 --> 00:23:35,950
Has everyone got mosquito repellent
that needs it?

321
00:23:35,950 --> 00:23:38,190
No, I haven't put it on yet.

322
00:23:38,190 --> 00:23:40,190
I've called in an old
expedition buddy

323
00:23:40,190 --> 00:23:42,910
and former Royal Marine Aldo Kane.

324
00:23:44,270 --> 00:23:48,190
He's the best in the business for
getting teams into difficult places,

325
00:23:48,190 --> 00:23:51,190
especially when ropes are involved.

326
00:23:51,190 --> 00:23:53,390
Eh, this is vile.
Can we go to the forest, please?

327
00:23:53,390 --> 00:23:54,430
Yeah.

328
00:23:54,430 --> 00:23:56,870
I think the smell is going to follow
us for a while, isn't it?

329
00:23:56,870 --> 00:24:00,710
Well, I'm used to being
on expeditions with you, so...

330
00:24:00,710 --> 00:24:02,110
THEY LAUGH

331
00:24:04,350 --> 00:24:05,790
Right, let's do this.

332
00:24:11,150 --> 00:24:15,350
It's over 35 degrees centigrade,
and approaching 90% humidity.

333
00:24:16,990 --> 00:24:20,270
Ahead of us is a gruelling trek
to Satelite.

334
00:24:21,510 --> 00:24:25,870
I reckon we probably won't cover
more than about 10km,

335
00:24:25,870 --> 00:24:29,150
six or seven miles on the map today,

336
00:24:29,150 --> 00:24:31,990
but it's going to take us
all day long.

337
00:24:31,990 --> 00:24:34,710
This is hard and heavy going.

338
00:24:36,110 --> 00:24:37,870
Oh!

339
00:24:37,870 --> 00:24:39,070
Are you all right?

340
00:24:41,550 --> 00:24:44,950
If Satelite is the gateway into
a larger network of passageways

341
00:24:44,950 --> 00:24:48,230
that we hope it is,

342
00:24:48,230 --> 00:24:51,350
we'll need to come back with
even more heavy air cylinders.

343
00:24:53,550 --> 00:24:58,310
Even so, Aldo's already
loaded with 50 kilos.

344
00:24:58,310 --> 00:25:02,670
Normally, every time we've been in
the jungle, what do we have?

345
00:25:02,670 --> 00:25:04,470
Jungle kit, hammock, food, water...

346
00:25:06,310 --> 00:25:11,990
Now we need jungle kit,
climbing kit, descending kit,

347
00:25:11,990 --> 00:25:14,190
diving kit... Yeah.
..pre-diving kit. Yeah.

348
00:25:15,670 --> 00:25:18,630
This explains why your load is
so ridiculous.

349
00:25:18,630 --> 00:25:20,710
BIRDS CHIRP

350
00:25:33,310 --> 00:25:35,310
MOTMOTS CHIRP

351
00:25:38,430 --> 00:25:42,670
Can you hear that sound, Aldo?
Say again? Can you hear that sound?

352
00:25:42,670 --> 00:25:45,670
What is it? Those are the birds that
live in the cenote.

353
00:25:45,670 --> 00:25:47,790
Ah, the motmot. We must be close.

354
00:25:49,350 --> 00:25:50,590
I hope so.

355
00:25:55,670 --> 00:25:57,070
Check that out.

356
00:25:59,390 --> 00:26:00,470
No way.

357
00:26:04,390 --> 00:26:05,710
It is huge.

358
00:26:08,310 --> 00:26:12,350
Robbie's been waiting a long time
for this opportunity.

359
00:26:13,750 --> 00:26:16,510
Could this 10m-wide opening
in the jungle

360
00:26:16,510 --> 00:26:19,110
be the doorway into
the Maya underworld

361
00:26:19,110 --> 00:26:21,910
and countless new passageways?

362
00:26:21,910 --> 00:26:24,270
Look how deep the water is
back there.

363
00:26:24,270 --> 00:26:26,790
It's all where the light hits it.
STEVE GASPS

364
00:26:26,790 --> 00:26:28,990
You couldn't even see it from there,
could you? No, no.

365
00:26:28,990 --> 00:26:31,030
We were circling over the top of
this, Robbie and I,

366
00:26:31,030 --> 00:26:34,390
with a helicopter and looking down.
We couldn't see it.

367
00:26:34,390 --> 00:26:36,950
I mean, it sort of
brings it home to you

368
00:26:36,950 --> 00:26:40,190
why this has not been done,
doesn't it?

369
00:26:40,190 --> 00:26:42,350
It still blows my mind
that you can find places

370
00:26:42,350 --> 00:26:43,710
that people haven't been.

371
00:26:43,710 --> 00:26:46,510
I want to get down there.

372
00:26:46,510 --> 00:26:48,670
You think anyone's ever been
in there before?

373
00:26:48,670 --> 00:26:50,510
No. Nobody.

374
00:26:50,510 --> 00:26:52,350
So what would your plan be?

375
00:26:52,350 --> 00:26:53,990
How are we going to tackle it?

376
00:26:53,990 --> 00:26:56,710
We'll be able to rig ropes
across there,

377
00:26:56,710 --> 00:27:00,470
all the way down that route,
basically. Yeah.

378
00:27:00,470 --> 00:27:01,990
I think, first things first,

379
00:27:01,990 --> 00:27:03,910
we need to get some water out of
there to drink.

380
00:27:03,910 --> 00:27:05,390
Yeah. Exactly.

381
00:27:05,390 --> 00:27:08,950
Yeah, I think we're
all out...all out of water.

382
00:27:08,950 --> 00:27:11,310
I'll just be careful with that.

383
00:27:12,670 --> 00:27:15,190
Just a few metres away,

384
00:27:15,190 --> 00:27:18,870
this hole also opens into Satelite.

385
00:27:18,870 --> 00:27:21,990
I haven't wanted water like this
for quite a while.

386
00:27:23,830 --> 00:27:25,910
This water drew the Maya here,

387
00:27:25,910 --> 00:27:29,510
and they might have even used
the same well.

388
00:27:32,710 --> 00:27:34,230
There we go.

389
00:27:38,150 --> 00:27:40,270
Is that nice? That's good.

390
00:27:40,270 --> 00:27:41,950
We've just kept it really simple...

391
00:27:41,950 --> 00:27:44,750
The plan is for Robbie and I
to recce the cave first

392
00:27:44,750 --> 00:27:46,990
by free-diving with just masks.

393
00:27:49,590 --> 00:27:51,670
We want to know there are
passageways here

394
00:27:51,670 --> 00:27:55,110
before we commit to exploring it
with air cylinders.

395
00:27:55,110 --> 00:28:00,390
I really, really want to know
if there's a cave passage here.

396
00:28:00,390 --> 00:28:02,390
The place is just so magical,

397
00:28:02,390 --> 00:28:05,590
and I've heard about it
since 20 years,

398
00:28:05,590 --> 00:28:09,910
and finally last year,
somebody was able to show it to me.

399
00:28:09,910 --> 00:28:12,630
It was always around like a ghost.

400
00:28:12,630 --> 00:28:16,030
Now we, first time,
are able to go down into it

401
00:28:16,030 --> 00:28:18,350
and see what's down there, it's...

402
00:28:18,350 --> 00:28:20,230
I can't wait.

403
00:28:20,230 --> 00:28:23,310
So you're going to be
free-hanging about here.

404
00:28:23,310 --> 00:28:25,070
Do you see the ropes there?

405
00:28:25,070 --> 00:28:26,430
Yeah.

406
00:28:26,430 --> 00:28:30,910
Now it's Aldo's job to get us
safely down the 20m drop,

407
00:28:30,910 --> 00:28:35,550
using rope access skills and a bit
of jungle improvisation.

408
00:28:35,550 --> 00:28:38,990
SB? Yeah? Are you happy with that?
Yeah. Right.

409
00:28:41,430 --> 00:28:42,430
The, erm...

410
00:28:43,670 --> 00:28:45,710
The logical part of my brain

411
00:28:45,710 --> 00:28:48,910
is telling me that this is
a phenomenal privilege

412
00:28:48,910 --> 00:28:50,430
and something just extraordinary

413
00:28:50,430 --> 00:28:53,230
that very few people will ever
get the chance to do.

414
00:28:53,230 --> 00:28:58,710
The illogical part of my brain is
imagining monsters and crocodiles

415
00:28:58,710 --> 00:29:01,710
and all kinds of other sinister
things down the bottom of that.

416
00:29:23,670 --> 00:29:25,590
OK. Here goes nothing.

417
00:29:25,590 --> 00:29:26,710
First man down.

418
00:29:36,910 --> 00:29:38,910
HIS VOICE ECHOES: Oh, wow!

419
00:30:06,670 --> 00:30:08,350
Oh, it's so creepy.

420
00:30:08,350 --> 00:30:10,390
Yeah.

421
00:30:10,390 --> 00:30:12,030
Rather you than me.

422
00:30:27,830 --> 00:30:28,870
I'm in.

423
00:30:31,230 --> 00:30:33,750
Oh, wow.

424
00:30:33,750 --> 00:30:35,830
This is seriously creepy...

425
00:30:46,990 --> 00:30:48,830
..but this is what it's
all been about.

426
00:31:00,990 --> 00:31:03,350
Right, Steve,
Robbie's coming down now.

427
00:31:22,310 --> 00:31:24,950
That's them both in the hole
at 4.30, OK?

428
00:31:35,390 --> 00:31:38,350
At last,
I'm in an unexplored cenote.

429
00:31:44,390 --> 00:31:47,110
We need to find out whether
this cavern has passageways

430
00:31:47,110 --> 00:31:48,670
leading away from it.

431
00:32:00,910 --> 00:32:04,230
It's an experience like none
I've ever had before.

432
00:32:21,670 --> 00:32:24,870
The first glimpse is tantalising,

433
00:32:24,870 --> 00:32:27,710
but we can't be sure what
lies beyond in the darkness.

434
00:32:29,150 --> 00:32:31,150
How far did you go in?

435
00:32:32,470 --> 00:32:34,430
It just goes on forever.

436
00:32:34,430 --> 00:32:37,230
It's huge and it's really deep.

437
00:32:38,430 --> 00:32:41,110
How deep? Can you guess how deep it
is there?

438
00:32:41,110 --> 00:32:43,670
Right here it's about 15m deep.

439
00:32:43,670 --> 00:32:46,070
Out to the sides
it could easily be 40,

440
00:32:46,070 --> 00:32:48,070
but you can't tell - you can't see.

441
00:32:48,070 --> 00:32:50,070
Yeah.

442
00:32:50,070 --> 00:32:53,910
OK, shall we head out
and make a plan?

443
00:32:53,910 --> 00:32:55,350
Yeah.

444
00:33:06,110 --> 00:33:08,510
I don't think I've ever seen you
look so excited.

445
00:33:09,830 --> 00:33:11,590
I don't know what to say.

446
00:33:11,590 --> 00:33:14,630
It is so much more than we expected.
So much more.

447
00:33:17,950 --> 00:33:21,110
OK, stop there. Stop. All stop.
All stop. All stop.

448
00:33:22,350 --> 00:33:24,910
That was a nice lift.
Thank you very much.

449
00:33:28,510 --> 00:33:30,510
What do you think? It's amazing.

450
00:33:30,510 --> 00:33:32,070
Better than you expected?

451
00:33:32,070 --> 00:33:34,510
Yeah, I'm really surprised.
It's amazing.

452
00:33:34,510 --> 00:33:36,790
Honestly, I've just...

453
00:33:36,790 --> 00:33:40,910
My brain is popping. I'm just
completely overwhelmed with it.

454
00:33:40,910 --> 00:33:44,670
It's... Incredible.
I don't have words.

455
00:33:44,670 --> 00:33:47,110
Well done. That was... Great.
Yeah, quite something.

456
00:33:54,470 --> 00:33:58,510
This cenote is much, much bigger
than anyone expected.

457
00:34:00,070 --> 00:34:02,190
It could have connecting passageways

458
00:34:02,190 --> 00:34:04,790
or it could just be
one vast, isolated cave.

459
00:34:07,750 --> 00:34:09,630
The only way to truly find out

460
00:34:09,630 --> 00:34:12,910
is to use air tanks and lights
to get a better look.

461
00:34:16,590 --> 00:34:18,830
For that, we'll have to wait
until morning.

462
00:34:21,750 --> 00:34:22,870
Look at that.

463
00:34:24,510 --> 00:34:28,030
There's around about 120,000
different kinds of moth

464
00:34:28,030 --> 00:34:32,670
found in the world, and the ones
around here are huge.

465
00:34:32,670 --> 00:34:36,870
Can you see? It's not just the moths
that get attracted by our lights -

466
00:34:36,870 --> 00:34:39,710
it's beetles like this chafer
as well.

467
00:34:39,710 --> 00:34:41,190
This is amazing.

468
00:34:41,190 --> 00:34:47,270
I've turned into a walking
wildlife-attracting machine.

469
00:34:50,710 --> 00:34:52,270
Ooh. Is that...?

470
00:34:57,430 --> 00:35:01,870
So, the Maya,
way back hundreds of years ago,

471
00:35:01,870 --> 00:35:05,350
still had very advanced astronomy,

472
00:35:05,350 --> 00:35:09,030
and they had names for all
the constellations in the heavens,

473
00:35:09,030 --> 00:35:12,790
and one of them
they called Scorpion,

474
00:35:12,790 --> 00:35:15,310
named after that curled tail

475
00:35:15,310 --> 00:35:20,270
and the constellations that
followed points along its length,

476
00:35:20,270 --> 00:35:23,830
and that is exactly the same
as the constellation Scorpio

477
00:35:23,830 --> 00:35:27,510
that the Romans and the Greeks
recognised.

478
00:35:27,510 --> 00:35:31,350
So these creatures
found a position in the heavens

479
00:35:31,350 --> 00:35:33,150
because of that curled tail.

480
00:35:44,310 --> 00:35:46,790
Morning.

481
00:35:46,790 --> 00:35:49,670
How did you sleep?
I slept like a baby.

482
00:35:51,230 --> 00:35:52,870
Really nice bit of forest.

483
00:35:52,870 --> 00:35:57,070
I was kind of lullabied to sleep
at night by the tree frogs,

484
00:35:57,070 --> 00:35:59,790
bats flapping through the trees
all night long,

485
00:35:59,790 --> 00:36:02,750
and then woke up this morning with
the calls of the motmots.

486
00:36:04,910 --> 00:36:06,790
Is that a stingy one?

487
00:36:06,790 --> 00:36:08,030
Yeah.

488
00:36:10,350 --> 00:36:11,950
Some of them in this part
of the world,

489
00:36:11,950 --> 00:36:14,470
if you get stung by them,

490
00:36:14,470 --> 00:36:18,070
you can still feel it
three months later. Ow.

491
00:36:18,070 --> 00:36:20,710
Yeah. You have a shower or you get
all sweaty or whatever

492
00:36:20,710 --> 00:36:25,870
and you rub yourself and the spines
that are embedded deep in your flesh

493
00:36:25,870 --> 00:36:28,830
start stinging all over again.

494
00:36:28,830 --> 00:36:30,230
That would hurt.

495
00:36:35,550 --> 00:36:38,430
This morning,
when we drop into Satelite,

496
00:36:38,430 --> 00:36:41,310
our camera operator Katy
will be critical

497
00:36:41,310 --> 00:36:43,630
to light and record what we find.

498
00:36:45,510 --> 00:36:47,350
That's you into
your main harness point,

499
00:36:47,350 --> 00:36:49,870
so when you get to the bottom,
spin that until it's red,

500
00:36:49,870 --> 00:36:51,190
pop that out,

501
00:36:51,190 --> 00:36:54,030
and then just leave that
at the bottom.

502
00:36:55,030 --> 00:36:58,950
It's a priority for her to use
one of our precious air cylinders,

503
00:36:58,950 --> 00:37:01,870
allowing her to explore deeper
with her camera.

504
00:37:03,190 --> 00:37:06,910
OK. Robbie and I will free-dive
around the dark edges.

505
00:37:06,910 --> 00:37:11,070
My first deep exploratory
scuba cave dive will have to wait.

506
00:37:11,070 --> 00:37:12,510
Going down.

507
00:37:12,510 --> 00:37:15,950
If Katy's camera and lighting rig
can help us find a passageway...

508
00:37:15,950 --> 00:37:17,590
Gently. Mm-hmm.

509
00:37:17,590 --> 00:37:20,390
..we'll all dive it again
with full scuba gear...

510
00:37:21,710 --> 00:37:23,030
OK.

511
00:37:26,110 --> 00:37:29,470
..but now we can finally see
the giant cenote...

512
00:37:34,310 --> 00:37:35,830
..in all its glory.

513
00:37:37,910 --> 00:37:39,310
Careful.

514
00:38:00,430 --> 00:38:02,670
Is the bottom of the rope clear?

515
00:38:02,670 --> 00:38:04,030
The rope is clear!

516
00:38:04,030 --> 00:38:05,310
Thank you.

517
00:38:05,310 --> 00:38:06,310
OK...

518
00:38:10,870 --> 00:38:12,190
Heads, look up!

519
00:38:28,070 --> 00:38:30,470
Yeah, that sounds like a good plan.

520
00:38:47,150 --> 00:38:52,230
With extra lighting, the magnitude
of this cenote is becoming apparent.

521
00:39:01,030 --> 00:39:02,990
These gigantic stalactites

522
00:39:02,990 --> 00:39:06,710
have taken hundreds of thousands
of years to form

523
00:39:06,710 --> 00:39:10,910
from the slow dripping of water
when this cave was dry.

524
00:39:23,310 --> 00:39:28,350
Though we're searching for signs
of connecting passageways,

525
00:39:28,350 --> 00:39:32,590
it's the underwater life
that draws our attention.

526
00:39:32,590 --> 00:39:36,870
Everything here is evolved for
life in a lightless world.

527
00:39:44,110 --> 00:39:48,150
These blind cave fish
don't react to torchlight.

528
00:39:53,190 --> 00:39:57,630
Instead, these predators sense
everything by vibration,

529
00:39:57,630 --> 00:39:59,190
including their prey.

530
00:40:03,550 --> 00:40:07,830
They're extremely rare
but, here, there are hundreds.

531
00:40:13,310 --> 00:40:18,390
The fresh water of the cenote may be
able to permeate the limestone,

532
00:40:18,390 --> 00:40:20,630
but it looks like there are
no holes big enough

533
00:40:20,630 --> 00:40:22,110
for these fish to escape.

534
00:40:26,590 --> 00:40:30,070
It's a sign that this is
an isolated cenote.

535
00:40:32,590 --> 00:40:34,990
All right, keep pulling.
Back in two.

536
00:40:37,030 --> 00:40:39,070
And all stop.

537
00:40:39,070 --> 00:40:45,790
It looks like it's just one
magnificent subterranean chamber,

538
00:40:45,790 --> 00:40:49,190
and our team were
the first down there.

539
00:40:49,190 --> 00:40:50,750
That's pretty special.

540
00:40:52,230 --> 00:40:58,590
But I think if we're looking to find
miles and miles of sunken cave
passage,

541
00:40:58,590 --> 00:41:01,070
I think we're going to have to
find somewhere else.

542
00:41:04,030 --> 00:41:09,550
It's been a huge achievement
to explore a new cenote,

543
00:41:09,550 --> 00:41:13,590
but as far as passageways
are concerned, it's a dead end.

544
00:41:13,590 --> 00:41:15,470
Our search goes on.

545
00:41:19,630 --> 00:41:24,350
Back in Tulum, Robbie's received
some important news.

546
00:41:24,350 --> 00:41:30,110
You remember that we did the water
samples at the beautiful cenote,

547
00:41:30,110 --> 00:41:33,470
you and Bernadette were diving,
with the full facemasks,

548
00:41:33,470 --> 00:41:34,990
with all the percolation coming out?

549
00:41:34,990 --> 00:41:37,110
Nohoch Kiin. Yeah, Nohoch Kiin.

550
00:41:37,110 --> 00:41:39,630
We did a sample there

551
00:41:39,630 --> 00:41:44,470
and it's really, really polluted
with chlorine.

552
00:41:44,470 --> 00:41:46,190
Chlorine?! Chlorine.

553
00:41:46,190 --> 00:41:49,390
But it's in the middle of
the forest - how did that happen?

554
00:41:49,390 --> 00:41:50,990
It must be connected to the town,

555
00:41:50,990 --> 00:41:53,830
because that's where
the chlorine comes in.

556
00:41:53,830 --> 00:41:57,910
When they pump the potable water
for Tulum from the wells,

557
00:41:57,910 --> 00:42:02,350
they put chlorine in it, so any
bacteria, everything would die,

558
00:42:02,350 --> 00:42:04,870
and that's the only way the
chlorine could come in there,

559
00:42:04,870 --> 00:42:10,910
and we are about, as the crow flies,
7km away from town.

560
00:42:10,910 --> 00:42:15,190
So, I mean, it must have flowed
through tens of kilometres of cave

561
00:42:15,190 --> 00:42:16,950
to get here from town. Yes.

562
00:42:16,950 --> 00:42:21,590
It goes like 7km as a straight line,

563
00:42:21,590 --> 00:42:25,110
and that would be probably
30km with caves,

564
00:42:25,110 --> 00:42:30,390
and the only place the pollution
could come from is from town. Right.

565
00:42:30,390 --> 00:42:33,830
So what kind of levels above normal
were the chlorine?

566
00:42:33,830 --> 00:42:35,830
Four times as high.

567
00:42:35,830 --> 00:42:38,710
Well, it shows that all of the
waterways are connected...

568
00:42:38,710 --> 00:42:41,510
Absolutely. ..and even when they're
quite a long way away from town,

569
00:42:41,510 --> 00:42:44,830
they're still receiving pollutants
from people.

570
00:42:44,830 --> 00:42:47,430
That's the most important thing of
our explorations now,

571
00:42:47,430 --> 00:42:49,830
that we can show this result,

572
00:42:49,830 --> 00:42:52,270
and find out the things to get,
in the long run,

573
00:42:52,270 --> 00:42:55,590
protection for the aquifer
and for the caves.

574
00:42:59,110 --> 00:43:00,990
This result is shocking,

575
00:43:00,990 --> 00:43:04,070
and it's all the more reason
to step up our efforts

576
00:43:04,070 --> 00:43:06,190
to find new cave connections.

577
00:43:12,070 --> 00:43:16,310
Part of Robbie's special talent
is studying satellite imagery...

578
00:43:20,150 --> 00:43:23,230
..looking for subtle differences
in vegetation

579
00:43:23,230 --> 00:43:26,630
or gaps in the canopy that could
reveal the presence of water

580
00:43:26,630 --> 00:43:28,470
and a new cenote.

581
00:43:32,990 --> 00:43:36,030
A few months ago,
he found just such a place

582
00:43:36,030 --> 00:43:39,030
and hiked there to check it out.

583
00:43:39,030 --> 00:43:41,070
It's a secret location.

584
00:43:41,070 --> 00:43:44,510
It has no name and no-one
has ever dived it.

585
00:43:45,950 --> 00:43:48,990
This is the opportunity to
get back on mission

586
00:43:48,990 --> 00:43:50,790
in our search for new caves.

587
00:44:08,350 --> 00:44:12,350
In the modern world,
if you want to be an explorer,

588
00:44:12,350 --> 00:44:14,430
you want to be a cave diver,

589
00:44:14,430 --> 00:44:18,870
but just prepare to do
a lot of carrying.

590
00:44:33,070 --> 00:44:35,310
Is this it?
This is it.

591
00:44:35,310 --> 00:44:38,350
What, seriously?
Seriously.

592
00:44:38,350 --> 00:44:40,750
Right in there,
there's a beautiful pool of water,

593
00:44:40,750 --> 00:44:42,430
crystal clear.

594
00:44:42,430 --> 00:44:46,070
I came here once before
and I did a free dive,

595
00:44:46,070 --> 00:44:48,950
just, like, with nothing,
just a mask and light,

596
00:44:48,950 --> 00:44:53,190
to see if there is an opening,
if there's a possible passage,

597
00:44:53,190 --> 00:44:55,630
and it looks really promising.

598
00:44:55,630 --> 00:44:58,630
Well, let's get in and have a look,
shall we? Let's have a look.

599
00:45:07,190 --> 00:45:09,830
OK, everyone, watch your heads
if you're coming in.

600
00:45:12,790 --> 00:45:16,950
Do you see that, the black hole
back there, down there? Yeah.

601
00:45:16,950 --> 00:45:19,590
That is the entrance.
That's where we want to go.

602
00:45:19,590 --> 00:45:22,830
So what's our plan here, Robbie?

603
00:45:22,830 --> 00:45:25,310
How do we go about tackling this?

604
00:45:25,310 --> 00:45:27,750
The first going in, which should be
me in this case,

605
00:45:27,750 --> 00:45:31,990
is installing the guideline,
so if stability goes bad,

606
00:45:31,990 --> 00:45:34,070
you only have to hold a line
in your hand

607
00:45:34,070 --> 00:45:37,110
and come back the way we came in.

608
00:45:37,110 --> 00:45:39,190
Are you sure we're going to
get in through there?

609
00:45:39,190 --> 00:45:43,590
Oh, yeah, we can fit through here,
right there.

610
00:45:43,590 --> 00:45:46,670
From there on,
I don't know what we'll find.

611
00:45:50,910 --> 00:45:54,310
That tiny passageway looks
scarily tight,

612
00:45:54,310 --> 00:45:58,550
but I'm overwhelmingly drawn
by what could be beyond.

613
00:46:01,270 --> 00:46:04,150
We're going to be the first
ones laying our eyes

614
00:46:04,150 --> 00:46:06,310
on that new cave there.

615
00:46:08,870 --> 00:46:14,030
It's just incredible.
It's a feeling you can't describe.

616
00:46:14,030 --> 00:46:18,510
Robbie, how's your half-mask
and your line-cutter?

617
00:46:18,510 --> 00:46:20,750
A little on the left side,
by the look of that.

618
00:46:20,750 --> 00:46:28,470
It's going to be fun to see Steve's
reaction to a virgin cave.

619
00:46:28,470 --> 00:46:31,070
It'll be interesting to see
how he handles that.

620
00:46:32,710 --> 00:46:39,950
Right now I've got a sense of
extraordinary excitement,

621
00:46:39,950 --> 00:46:47,310
but that excitement is tinged
with nervousness, you know?

622
00:46:47,310 --> 00:46:49,070
This is what all the
training has been for.

623
00:46:49,070 --> 00:46:51,310
This is what it's been
working up to,

624
00:46:51,310 --> 00:46:53,710
is getting in there and exploring.

625
00:46:58,470 --> 00:47:00,390
Yeah, now I just have to
get my head right.

626
00:47:21,590 --> 00:47:24,110
Pouch there, and that's got
a spare light in it.

627
00:47:24,110 --> 00:47:25,350
One spare light.

628
00:47:25,350 --> 00:47:27,910
I've got another spare light
in here. That's OK.

629
00:47:27,910 --> 00:47:29,950
Line arrows and cookies
are on your butt.

630
00:47:29,950 --> 00:47:31,430
Yeah. All good. Awesome.

631
00:47:32,870 --> 00:47:35,550
I'm running through all
my mental checklists,

632
00:47:35,550 --> 00:47:37,550
and making sure I've got everything.

633
00:47:37,550 --> 00:47:40,950
What's that?
Oh, do you want me to use it?

634
00:47:40,950 --> 00:47:44,030
We've now got me,

635
00:47:44,030 --> 00:47:46,350
Katy, the dive cameraperson,

636
00:47:46,350 --> 00:47:49,790
and her support diver,
so four of us in this cave,

637
00:47:49,790 --> 00:47:52,750
and every single extra person
that you add

638
00:47:52,750 --> 00:47:55,190
adds an extra level of complication

639
00:47:55,190 --> 00:47:57,830
and an added possibility of
something going wrong.

640
00:48:01,470 --> 00:48:05,510
If something goes wrong in cave
diving, it goes wrong in a big way,

641
00:48:05,510 --> 00:48:08,830
and everything happens quickly

642
00:48:08,830 --> 00:48:10,750
and can be over fast.

643
00:48:15,670 --> 00:48:18,430
OK. How can we best do this?

644
00:48:19,710 --> 00:48:23,910
We would use one third of the air
to go into the cave,

645
00:48:23,910 --> 00:48:28,390
one third of the air in our tanks
for the way back,

646
00:48:28,390 --> 00:48:33,110
and one third of the air
for the event of an emergency.

647
00:48:34,750 --> 00:48:37,430
If anything goes wrong
during that dive,

648
00:48:37,430 --> 00:48:40,710
we will call the dive,
and we go straight out,

649
00:48:40,710 --> 00:48:43,110
back out to the exit, right?

650
00:48:43,110 --> 00:48:44,390
Is that good? Is that clear?

651
00:48:44,390 --> 00:48:45,710
Yeah.

652
00:48:45,710 --> 00:48:47,950
All right. Right. Let's do this.

653
00:48:47,950 --> 00:48:48,990
Lead the way.

654
00:49:08,590 --> 00:49:10,390
That's the left tank.
That's the left tank?

655
00:49:10,390 --> 00:49:12,190
That should be right?
This is the left tank.

656
00:49:12,190 --> 00:49:14,030
That's the left tank.
That's the right.

657
00:49:18,430 --> 00:49:19,510
Yep.

658
00:49:27,470 --> 00:49:30,030
All right, everybody happy?

659
00:49:30,030 --> 00:49:32,030
Can we go? Are you ready?

660
00:49:32,030 --> 00:49:33,550
Happy as I'll ever be.

661
00:49:33,550 --> 00:49:36,110
Marty? Let's go. Katy? Yeah.

662
00:49:36,110 --> 00:49:37,710
All right, then, let's do this.

663
00:50:29,150 --> 00:50:31,550
Katy, we are calling the dive
and going up!

664
00:50:34,110 --> 00:50:39,550
HEAVY BREATHING

665
00:50:54,110 --> 00:50:57,430
That was proper sketchy.

666
00:50:57,430 --> 00:51:00,230
What happened?

667
00:51:00,230 --> 00:51:02,230
I didn't see anything.

668
00:51:02,230 --> 00:51:07,110
No. Just absolute zero visibility.

669
00:51:07,110 --> 00:51:08,750
That wasn't good.

670
00:51:14,070 --> 00:51:15,710
So here's what I'm going to do.

671
00:51:15,710 --> 00:51:18,830
I'll go back down there,
I'll find my reel,

672
00:51:18,830 --> 00:51:21,350
and then I'll come back to
get you guys.

673
00:51:24,630 --> 00:51:28,190
Robbie is going alone to check
the lifeline is still in place.

674
00:51:30,710 --> 00:51:34,750
As dive leader, it's his call
whether we make a second attempt

675
00:51:34,750 --> 00:51:36,350
to push through the silt cloud.

676
00:51:37,390 --> 00:51:40,470
Was it disorientating quite quickly?

677
00:51:40,470 --> 00:51:43,310
Super disorientating.

678
00:51:43,310 --> 00:51:46,750
It's probably the thing, more than
anything else I've ever done,

679
00:51:46,750 --> 00:51:49,990
that makes you want to
panic quicker.

680
00:51:49,990 --> 00:51:51,550
I'm not a panicky person,

681
00:51:51,550 --> 00:51:54,430
but you just feel your heartbeat
just start to go up

682
00:51:54,430 --> 00:51:59,070
and your breathing start to go up,
and the mist descends.

683
00:52:10,870 --> 00:52:12,910
All good? All good.

684
00:52:12,910 --> 00:52:17,030
Me, Steve, Katy, Marty...

685
00:52:17,030 --> 00:52:20,110
You guys, please keep your
feet still, all right?

686
00:52:20,110 --> 00:52:21,710
Don't move too much,

687
00:52:21,710 --> 00:52:24,310
because that's what silted out
the whole place in the first place.

688
00:52:24,310 --> 00:52:25,510
Right?

689
00:52:25,510 --> 00:52:27,350
Keep the line in your hand.

690
00:52:30,790 --> 00:52:31,750
OK.

691
00:52:32,950 --> 00:52:38,950
We're going in again, to try to
push through that silt cloud

692
00:52:38,950 --> 00:52:41,350
and see what's on the other side.

693
00:52:42,790 --> 00:52:45,230
Steve, do you copy? Steve?

694
00:52:46,510 --> 00:52:47,870
Yeah, I can hear you.

695
00:52:49,310 --> 00:52:51,670
I still have zero visibility here.

696
00:52:51,670 --> 00:52:54,150
I'm just keeping a really good hold
on the line.

697
00:52:56,630 --> 00:52:59,990
That's perfect.
I hear you loud and clear.

698
00:52:59,990 --> 00:53:01,190
Say again?

699
00:53:02,630 --> 00:53:04,750
Steve, do you still copy? Steve?

700
00:53:11,390 --> 00:53:14,070
Nah, now they're beyond
the abilities

701
00:53:14,070 --> 00:53:16,270
of this communication system.

702
00:53:16,270 --> 00:53:18,270
Who knows how far inside they are
right now?

703
00:53:18,270 --> 00:53:20,550
We have no way to know
until they come back out.

704
00:53:23,390 --> 00:53:26,710
Ugh, it's zero visibility.

705
00:53:26,710 --> 00:53:28,910
Just squeezing myself in...

706
00:53:34,710 --> 00:53:37,430
I can see Robbie's torch
ahead of me.

707
00:53:44,350 --> 00:53:47,590
I think the water may be
starting to clear a little.

708
00:53:49,630 --> 00:53:50,710
Yes!

709
00:53:53,110 --> 00:53:55,510
The visibility's starting to
open out!

710
00:54:08,910 --> 00:54:10,870
What an experience!

711
00:54:12,590 --> 00:54:14,190
Absolutely no idea...

712
00:54:17,630 --> 00:54:20,270
..what's off there in the darkness.

713
00:54:40,830 --> 00:54:42,830
Oh, this is tight.

714
00:54:45,470 --> 00:54:47,310
I'm totally not built for this.

715
00:55:05,390 --> 00:55:09,110
We're several hundred metres in,

716
00:55:09,110 --> 00:55:12,670
and we might as well be on
the surface of the moon.

717
00:55:14,750 --> 00:55:18,990
It's just essential
that nothing goes wrong now.

718
00:55:25,510 --> 00:55:27,630
Robbie seems like he's found
another lead.

719
00:55:52,110 --> 00:55:54,710
This is absolutely magical.

720
00:56:00,790 --> 00:56:03,910
The formations are just dazzling.

721
00:56:16,350 --> 00:56:21,990
Absolutely endless amounts of
stalagmites and stalactites.

722
00:56:21,990 --> 00:56:27,270
They were formed here
when this was dry cave,

723
00:56:27,270 --> 00:56:31,910
and the thought that we're the
first people ever to see them

724
00:56:31,910 --> 00:56:33,630
is almost beyond belief.

725
00:56:33,630 --> 00:56:35,390
It's totally overwhelming.

726
00:57:01,670 --> 00:57:04,230
In this first phase of
the expedition,

727
00:57:04,230 --> 00:57:07,270
we've explored new cenotes

728
00:57:07,270 --> 00:57:09,870
and we've documented
new passageways.

729
00:57:16,230 --> 00:57:19,670
Mapping this vast web of
freshwater cenotes

730
00:57:19,670 --> 00:57:21,590
will help scientists
better understand

731
00:57:21,590 --> 00:57:24,110
how far pollution is spreading.

732
00:57:28,870 --> 00:57:33,070
Protecting this fragile environment
and its precious resource...

733
00:57:33,070 --> 00:57:36,390
STEVE SHOUTS JOYFULLY

734
00:57:36,390 --> 00:57:38,590
..should now be a top priority.

735
00:57:40,150 --> 00:57:42,190
Robbie, thank you so much.

736
00:57:42,190 --> 00:57:43,790
ROBBIE LAUGHS

737
00:57:43,790 --> 00:57:46,350
That was... That was good.
..unbelievable.

738
00:57:53,590 --> 00:57:57,710
Next time, we push further
into the Yucatan caves

739
00:57:57,710 --> 00:57:59,670
on the trail of the Maya...

740
00:57:59,670 --> 00:58:01,950
We've got a long, long way to go.

741
00:58:01,950 --> 00:58:04,430
..uncovering ancient artefacts,

742
00:58:04,430 --> 00:58:07,150
human remains
and sinister secrets...

743
00:58:07,150 --> 00:58:09,030
It is the stuff of nightmares.

744
00:58:09,030 --> 00:58:12,470
..and I face my most terrifying
underwater challenge yet.

745
00:58:14,910 --> 00:58:16,270
HE SCREAMS