We visit some of the World's most extensive cave systems:
- Lechuguilla Cave in Carlsbad Caverns National Park, New Mexico
- Niah Great Cave on Sarawak, Malaysia, a World Heritage Site
- Jillabenan and Yarragobilly Caves in Australia
- Postojna Cave, Slovenia's most extensive cave system
Also seen are fossilized dinosaurs, and volcanic lava formations.
