Fodor's Expert Review Wind Cave
Known to American Indians for centuries, Wind Cave was named for the strong currents of air that alternately blow in and out of its entrance. The cave's winds are related to the difference in atmospheric pressure between the cave and the surface. When the atmospheric pressure is higher outside than inside the cave, the air blows in, and vice versa. With more than 145 miles of known passageway divided into three different levels, Wind Cave ranks the sixth longest in the world. It's host to an incredibly diverse collection of geologic formations, including more boxwork than any other known cave, plus a series of underground lakes. The cave tours sponsored by the National Park Service allow you to see unusual and beautiful formations with names such as popcorn, frostwork, and boxwork.