Wind Cave National Park
Hot Springs, SD · Black HillsFree
Boxwork, rarely found anywhere else in the world, hangs from the ceilings of Wind Cave in South Dakota and lines many of its walls. In 1903 this became the eighth national park…

Photo: Murray Foubister / CC BY-SA 2.0 · source
Jewel Cave, 13 miles west of Custer in the Black Hills, takes its name from the calcite crystals crusting its walls, the kinds called nailhead and dogtooth spar. More than 220 miles have been mapped, making it the second longest cave in the country, and the survey isn't finished. On the Scenic Tour an elevator drops you to a lit half-mile loop past flowstone and the ribbons rangers call cave bacon. The Historic Lantern Tour takes the rough early passages instead, with a lantern in your hand. Air rushes in and out of the cave as the pressure outside rises and falls.