Jewel Cave National Monument protects Jewel Cave, mapped to 220.33 miles of passageway as of July 2025, making it the fifth longest cave in the world and the second longest in the United States. It lies about 13 miles west of the town of Custer in the Black Hills of South Dakota. The cave became a national monument in 1908, the first ever established specifically to protect a cave. Jewel Cave is notable as one of the best known examples of a breathing cave, in which changes in outside air pressure drive air into and out of its passages, and it takes its name from the calcite crystals that coat many of its walls. The monument covers 1,273 acres and is administered by the National Park Service, drawing about 145,000 visitors in 2024.
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