The Earth's large, deep calcareous caves are virtually inaccessible and therefore barely explored - requiring expert diving where flooded. Some of its wildlife is as strange and specific as in the deep, darkest part of the ocean, whether physically adapted -notably to the dark. Nevertheless, some caves(did) play an important part in native cultures, even as sources of fresh water for some Mayan cities.
Stars: David Attenborough, Sigourney Weaver, Huw Cordey
Director(s): Alastair Fothergill
Writer(s): David Attenborough, Gary Parker