Jewel Cave National Monument

Jewel Cave National Monument, located 13 miles west of Custer on US-16 in the Black Hills of South Dakota, contains the third-longest cave system in the world with over 220 miles of surveyed passages. The cave takes its name from the calcite crystite crystal formations — sometimes called jewels — that line the walls of many chambers and give them a sparkling appearance. The speleothem inventory at Jewel Cave is extraordinarily diverse: nailhead spar, dogtooth spar, hydromagnesite balloons, cave bacon, cave flowers, and frostwork create formations rarely found together in a single system. Three tour options are available through the National Park Service. The Scenic Tour (1 mile, electrically lit, elevator access from surface) is the most accessible. The Historic Lantern Tour follows original exploration routes from the 1900s using only handheld lanterns to illuminate the passage. The Spelunking Tour provides off-trail crawling experiences through undeveloped passages for those seeking a more physical underground experience. All tours depart from the visitor center and require advance reservation in summer, when demand reliably exceeds available slots. The cave maintains a constant 49°F (9°C) and moderate humidity regardless of surface conditions; a warm mid-layer is essential year-round. Because the cave system continues to reveal new passages with each exploration season — park staff discovered over 25 miles of new passages in one recent decade — Jewel Cave is considered one of the most dynamic exploration caves open to the public in the United States. The surrounding Black Hills ponderosa pine landscape provides a pleasant setting for brief surface walks near the visitor center.