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 U.S.A. is 193km long with astonishing crystal formations. Caves are remarkable habitats with equally bizarre wildlife. Cave angel fish cling to the walls behind waterfalls with microscopic hooks on their fins. Cave swiftlets navigate by echo-location and build nests out of saliva. The Texas cave salamander has neither eyes nor pigment. Planet Earth gets unique access to a hidden world of stalactites, stalagmites, snotites, and troglodytes.

Originally released by BBC Worldwide Learning, 2006. Streaming video file encoded with permission for digital streaming by Infobase on April 20, 2018.

Caves: Introduction (2:50); --Food in Caves (3:54); -- Geology of Caves (3:09); -- Cave Ecology (6:45); -- Cave Resources (3:29); -- Cave Formations (2:40); -- Underwater Caves (8:23); -- Cave Specialists (5:49); -- Deadly Acid Caves (3:36); -- Hidden Caves of Lechuguilla (6:58); -- Credits: Caves (1:00); .