13622 Highway 40
Keystone, South Dakota 57751
Discovered by placer miners in 1876 and opened to the public in 1927, Rushmore Cave in the Black Hills is the 2nd largest cave system in the United States. Containing "the legendary big room," icicle-like stalactites, fossils, massive flowstones and spires of stalagmites, Rushmore Cave began forming 60 million years ago. Open May through October, guided tours last about one hour.