Jewel Cave is one of the few caves in South Dakota that is managed by the National Park Service. And for good reason; Jewel Cave is the third longest cave in the world, with 202 miles of explored underground passageways. The entrance to the cave is located within the bounds of the national monument, however, more than 55% of the underground tunnels lie outside the bounds, beneath the Black Hills National Forest. Only a 30 minute drive from Lantern Inn, you can explore these unique caverns and parts of Black Hills National Forest in one day.