Wind Cave

Declared in 1903, it is the sixth oldest national park in the world and the first created specifically to protect a cave. Its interior holds 95% of all the boxwork known on the planet, a honeycomb mineral formation of thin calcite fins that is extremely rare outside this cave. The Lakota people hold the cave's natural entrance, where the wind audibly moves in and out as the atmospheric pressure changes, to be the sacred place of origin of their people and of the bison.