Historic Entrance Guided Tour at Mammoth Cave National Park, Kentucky

Mammoth Cave is the longest cave system in the world (over 360 miles, 580 km.) It became a U.S. National Park in 1941, and a World Heritage Site in 1981. National Park guides lead underground tours that range from 30 minutes to 6.5 hours. The Historic Entrance tour takes 2 hours and is 2 miles (3.5 km.) in length. A cool blast of air marks the entrance point, and a dimly-lit set of stairs leads down into a series of tubular caverns that are larger than an average subway (Tube, Metro, 地下鉄) station. Deep in the cave, a catwalk crosses the so-called Bottomless Pit, and at Fat Mans Misery a low cave roof forces visitors to crouch along a narrow single-file path. Finally, the cave entrance is regained via a steel staircase tower of over 130 steps.