South Dakota: An Underground Maze
Credit: Illustration by Kagan Mcleod

Jewel Cave National Monument is more than 166 miles of underground labyrinth, named for its calcite crystal walls. On the Wild Caving Tour, you trek through an 8.5-inch crawl space and up 90-degree chutes. But the most intense part is Hurricane Corner, where a 35-mile-per-hour barometric wind screams through the blackness.

Getting there: From the airport in Rapid City, drive 50 miles to the $27 Wild Caving Tour, open from the end of May to the end of October and monthly during the off-season.