After visiting Carlsbad Caverns earlier in the week, the Mammoth Cave (both a National Park and a World Heritage Site) does not initially seem quite as impressive.  It contains a small fraction of the speleothems which are to be found in the former.  What is amazing is the sheer scale of the cave.  With 405 miles of surveyed passageways Mammoth Cave is by far the world’s longest known cave system, over twice as long as the second-longest cave system, Mexico’s Sac Actun underwater cave, a portion of which Kyle and I explored during his coming of age adventure.