Jewel Cave National Monument (http://nps.gov/jeca/) is in the Black Hills of South Dakota. The cave is the second longest known cave in the world, and going. In 2006 more than 136 mi 219 km of passage have been surveyed. The cave received its name after the large amounts of calcite calcium carbonate crystals found in the cave. The cave offers plenty of underground beauty, however, offers a variety of things to do on the surface.
