Javiere Navarette - The Labyrinth

Mammoth Cave is the longest known cave system in the World. It was also historically the second major tourist attraction in the United States (after Niagara Falls).

When I was living in Nashville, I frequently took a day trip over to Mammoth Cave about 2 hours away. I took several of the cave tours, wandered through forgotten areas of the park, and was once held at gunpoint by a park ranger. Fun times.

Mammoth Cave is actually a pretty ugly cave, and that's because it is a dry, relatively static limestone cave capped by a layer of sandstone. Water has difficulty getting under the cap, and so tends to cut through in large vertical shafts, then extend horizontally through the weaker limestone areas, creating long passageways with minimal formations (which can be seen as the cave actively dissolving, like melting candlewax). It is nevertheless quite fascinating geologically. Mammoth Dome is one of the highlights of the Historic Tour, a large, 61m high vertical shaft that requires a staircase to ascend.

Courtesy of  theroguez!