Humans like to think that once they've climbed a mountain, they've somehow conquered it. But they can only ever be visitors to this alien, frozen world. This week, Planet Earth takes you on a tour of itsmightiest ranges, beginning with the birth of a mountain at one of the lowest places on earth, and ending at the summit of Everest. Unprecedented access brings you closer than ever before to the most awe-inspiring mountain landscapes on our planet, and the secretive, almost mythical creatures that inhabit them - the "real" mountaineers.

In Ethiopia, Planet Earth ventures into the heart of a volcano to discover one of earth's rarest phenomena - a lava lake that's been erupting for over a hundred years. The same forces created Ethiopia's Simien Mountains, home to troops of gelada baboons nearly a thousand strong. In the Andes, a family of five puma struggle to survive the most unstable mountain weather on the planet.

Experience the full force of an avalanche in the Rockies, where grizzlies survive the harsh winters deep inside the dangerous slopes. In summer, the bears climb the peaks in search of moths which they devour by the thousand.

Descend into the icy core of a glacier in the Alps and emerge in Pakistan, at the snout of the largest glacier on earth. This realm of giant peaks is home to the highest land predator on the planet - the snow leopard. Astounding images of a female snow leopard hunting to feed her cub are a world first.

Enter a mountain cave in China for the first ever glimpse of a wild giant panda mother nursing her week-old baby, and fly alongside demoiselle cranes as they attempt to cross the largest range on our planet, the Himalayas. The cranes, like all visitors to the hostile world of the high mountains, dare not linger.

The Cave of Swallows in Mexico is a 400-metre vertical shaft. It's deep enough to engulf the Empire State Building, yet few people even know of its existence. Caves are earth's final frontier and this programmegoes where few have been before.

Deer Cave in Borneo is a daytime retreat for five million bats; their droppings support an entire community of creatures. Shine a light on one massive pile of droppings and the whole place shimmers with millions of dung-eating insects.

Caves also harbour some of the most remarkable and bizarre animals on earth; from cave swiftlets who build nests out of just saliva to the troglodytic animals that never see daylight or ever set foot on the surface. Troglodytes like the Texas cave salamander and Thailand's cave angel have neither eyes nor pigment, and the entire populations of both are found in just a couple of caves.

From Lechuguilla Cave's astonishing six-metre-long crystals to the extraordinary snottites of Villa Luz, this documentary provides unprecedented access to the hidden world of caves.