Cave
Jewel Cave National Monument
58 locals recommend
Location
11149 US-16
Custer, SD
Tips from locals
Make reservations on the summer online. Has crystals,  and most cave formations, including large caverns. Is one of the longest caves in the world.
This is the third longest cave in the world and is administered by the National Park Service. I'd highly recommend the scenic tour which is moderately strenuous and lasts about 1 hour 20 minutes.
Jewel Cave National Monument is not only the third-longest cave in the world (currently 141.37 miles!), it is also one of its most structurally complex. Located just over an hour southwest of Rapid City, Jewel Cave is a regional gem tucked in the Black Hills.