#2 Jewel Cave (South Dakota)
In the South Dakotan Black Hills, there is so much great stuff to see above ground that it seems unthinkable that there is also cool stuff to see below ground. Oh, surprise! A national monument since 1908, Jewel Cave is the third-longest cavern system on the planet, with more than 180 miles of documented and inspected passageways.
The cave lives up to its name, with massive calcite crystals coating the ceilings and walls that resemble dripping jewels (there is also a 10-foot-long chunk of flowstone known as “cave bacon”). Three distinct guided tours through the tunnels are available, ranging in difficulty from easy to difficult.
Each season has a different tour schedule. Scenic Tours is the only one that accepts bookings in advance; all others are first-come, first-served.
