The 6th largest and densest cave system in the world.
Established in 1903, Wind Cave National Park is home to over 140 miles of mapped cave passages. The cave features 95% of the world's known boxwork calcite formations and got its name from the sound of rushing wind created at its few small openings.
A guided tour is the only way to see the cave system unless you are in the park's limited volunteer cave exploring group. Depending on the time of year, up to 5 different tours are offered: nps.gov/wica/planyourvisit/schedule.htm. Tickets are only available the same day on a first-come-first-serve basis.