Mammoth Cave National Park
Wow Factor: The longest cave system in the world, with 390 miles of interconnected passages and rooms, named for its massive underground cathedrals.
You'll Love If: You think head-lamps are cute.
Explore It: The Violet City Lantern tour re-creates the cave's original guided tours from the mid-1800s on a lantern-lit walk ($15). nps.gov/maca