Part 1: Natural Wonders - Nature's underworld is an ominous, alien landscape, inspiring nightmares, myths and legends. By challenging our fears and penetrating the dark we discover amazing sights and creatures. See the breathtaking deep cave paintings made by early humans. Wonder at the eerie light created by millions of tiny creatures in a New Zealand cavern. Travel with divers to explore a treacherous underground sea in the Yucatan. Be there as scientists discover a frozen lake that's been closed off for millions of years, perhaps containing ancient life forms. Enter a deep African cave with elephants and other plains animals as they ignore all risk in their search for essential salts. Caves with millions of bats, and sightless, colorless weird creatures, eerie catacombs and their gruesome inhabitants, glorious crystal caves, all this and more in the Natural Wonders section of Amazing Secrets of Our World.