Skyline Caverns, on US 340 near the entrance to Skyline Drive, attracts many visitors each year. Discovered in 1937, it is the site of the world's only known calcite formations dubbed "anthodites" - six-sided crystals with white spikes that spread out in all directions. The growth rate of these formations, called "the orchids of the mineral kingdom," is estimated to be only 1 inch every 7,000 years!