Wind Cave National Park

Wind Cave National Park in the southern Black Hills of South Dakota protects one of the world's longest cave systems — over 150 miles of mapped passages — as well as 33,847 acres of mixed-grass prairie and ponderosa pine forest above ground. The cave is named for the atmospheric pressure-driven wind that blows in and out of the natural entrance as surface pressure changes; early visitors reported the phenomenon before any exploration had taken place. The most distinctive geological feature inside is boxwork, a honeycomb of thin calcite fins projecting from the cave walls; Wind Cave contains the world's greatest concentration of this rare formation. The National Park Service operates five guided tours ranging from the accessible Garden of Eden Tour (paved route, 1 hour) to the off-trail Wild Caving Tour (4 hours, requires advance reservation and sturdy clothing). The Scenic Tour, the park's most popular option, covers electrically lit passages including chambers dense with boxwork. The aboveground prairie is one of the few intact mixed-grass grassland ecosystems remaining in the Great Plains and hosts bison, elk, pronghorn, coyotes, and black-footed ferrets. Prairie Dog Town near the north entrance draws regular wildlife viewing crowds. The cave temperature holds at a constant 53°F (12°C) year-round regardless of surface conditions, making a light jacket essential even in the height of summer. All cave tours depart from the visitor center and are capped in size; the most popular tours sell out days or weeks in advance during the summer season.