The Cave of Swallows in Mexico is a 400m vertical shaft, deep enough to engulf the Empire State Building. The Lechuguilla cave system in the USA is 193km long and 500m deep with astonishing crystal formations hanging from its chambers. Although often overlooked, caves are remarkable habitats with equally bizarre wildlife. Cave angel fish cling to the walls behind cave waterfalls with microscopic hooks on their flattened fins. Cave swiftlets navigate by echo-location and build nests out of saliva. The Texas cave salamander has neither eyes nor pigment. Unique access to a hidden world of stalactites, stalagmites, snotites and troglodytes brings a wealth of surprises.
As almost all animal inhabitants of Antarctica are forced to migrate north, the sea underneath the frozen ice still provides a home to many specially adapted fish whose cells are protected from freezing through an "antifreeze" liquid. Many of them feed on the faeces of other animals. The most notable larger animal that does not migrate north is perhaps the Weddell Seal, which can be found as close as 1300 kilometres to the pole. Groups of seals tear holes into the ice to dive for food and come up to breathe. The females come back to the ice to give birth.
Africa's largest herd of elephants and a fearless pride of young lions come face to face in an epic fight for survival. Rarely do their worlds collide, until now. This is no chance conflict; nature has played its part. Drought has weakened the elephants, and the lions are desperately hungry. The dawn of the giant killers has arrived.