Jewel Cave

Beneath about four square miles of Black Hills forest, Jewel Cave packs more than 220 miles (354 km) of mapped passage, second only to Mammoth Cave in the United States and among the longest caves known anywhere. Brothers Frank and Albert Michaud found it in 1900 when they felt cold air blowing from a small hole in Hell Canyon, west of Custer, South Dakota. They blasted the entrance wider and named the cave for the glittering calcite crystals lining its walls, the jewels that still give it its name.

President Theodore Roosevelt proclaimed Jewel Cave a national monument on February 7, 1908, the first created to protect a cave. For decades it seemed modest. Then in 1959 rock climbers Herb and Jan Conn began exploring and mapped more than 64 miles by 1979, and volunteer survey teams have extended it ever since. The cave breathes, with air rushing in or out as surface pressure changes, a sign that much remains undiscovered. Its temperature holds near 49°F (9°C), and visitors enter only on ranger-led tours.

• South Dakota
  The Mount Rushmore State, plains, badlands, and Black Hills located in
• Mount Rushmore
  The 60-foot presidential faces carved into the Black Hills near
• Wind Cave National Park
  Black Hills park of boxwork caves and bison prairie near
• Lechuguilla Cave
  The sealed, pristine cave beneath Carlsbad Caverns National Park related
• Mammoth Cave National Park
  Kentucky park above the longest known cave system on Earth related