United States
43.7290°, -103.8290°
1908
5.27
Jewel Cave National Monument protects the world's third-longest known cave system with over 200 miles of mapped passages. The cave is renowned for its calcite crystal formations that sparkle like jewels, giving the cave its name. Above ground, the monument preserves ponderosa pine forest and mixed-grass prairie ecosystems. The monument is managed by the National Park Service.