Wind Cave

Wind Cave, located in the rugged Black Hills of South Dakota is one of the world's longest and complex cave. It was named for its very strong air currents that pass in and out of its entrance. Changes in barometric pressure rises apparently trigger these eerie winds. When the atmospheric pressure rises outside the cave, wind rushes in; then when the outside air pressure drops, the air rushes out again.
Wind Cave is remarkable for its unrivaled displays of the delicate rock formation known as Boxwork - The nature's intricate art wonders!. Boxwork is found in small amounts in other caves, but perhaps in no other cave in the world is boxwork so well-formed and abundant as in Wind Cave. [Boxwork is made of thin blades of calcite that project from cave walls and ceilings, forming a honeycomb pattern.] When the limestone containing the cave was uplifted some 60 million years ago, it was broken up by networks of intersecting cracks. Over long periods of time, seeping water deposited veins of the mineral calcite in the cracks. Later, when the cave was formed, the enveloping limestone was eroded away, while the more resistant calcite in the cracks was left projecting from the ceilings and walls in fragile, beautifully intricate patterns.
The Wind Cave National Park has a number of unusual attractions above the ground as well, 28,295 acres of mixed-grass prairie, ponderosa pine forest, and associated wildlife are the main features of this park.