Hiking in Mammoth Cave National Park can be a fun and rewarding experience as in other national parks. It is a great way to both see and experience the park. Mammoth Cave, as its name suggests, is the world's most extensive cave system, with 300 miles of passages that are known and more that have not been explored. Located in central Kentucky, this subterranean phenomenon was created more than several million years ago as water worked its way through limestone deposits, dissolving the rock and carving underground passageways to connect with the nearby river. Over the ages, the water table slowly dropped leaving narrow horizontal tunnels, broad caverns and giant vertical shafts linked in a many-leveled labyrinth. The lower passage ways are still being enlarged by streams and rivers. Water seeping into the cave creates stalactites, stalagmites and white gypsum crystal formations that decorate some of the passages and rooms. Rare and unusual animals, such as blind fish and colorless spiders, demonstrate adaptation to the absolute blackness and isolation. Having evolved over millennia, 50 species of cave creatures are now threatened by pollutants that are entering the cave system from today's water supply. Mammoth Cave is an incredible natural phenomenon that continues to challenge humankind. (Inscribed in 1981)