Mammoth Cave is the most extensive cave system in the world, with more than 365 surveyed miles of cave passageways, perhaps as much still to be discovered.
The flora and fauna of Mammoth Cave is the richest cavernicolous wildlife known; of the more than 130 species documented in the cave, 12 are eyeless, unpigmented cave dwellers such as fish, crayfish, beetles, and harvestmen. It is of geological importance due to the 10 million years of cave-forming action by the Green River and its tributaries; nearly every type of cave formation is known within this site, and the geological processes involved in cave formation are continuing. Long passages with huge chambers, vertical shafts, stalagmites and stalactites, gypsum "flowers" and "needles", and other natural features of the cave system are all superlative examples of their types.
Outside the cave, the karst topography is superb, with fascinating landscapes, luxuriant vegetation, and abundant wildlife; all of the features of a karst drainage system - vast recharge area, complex network of underground conduits, sinkholes, cracks, fissures, and surface and underground springs - are found within the site.