Skyline Caverns, is a series of geologic caves and a tourist attraction located in Front Royal, Virginia. The caverns were discovered by Walter S. Amos, a retired geologist and mineralogist from Winchester, Virginia, on December 17, 1937. The Skyline Caverns is open year-round, offering guided tours through the caverns. In addition to the cavern tours, attractions include a miniature train ride and mirror maze. 
Amos was contracted by several private and government agencies to search for caves and caverns to open in conjunction with Skyline Drive. During his search, he came across the current parking lot of the caverns, which he noticed was in the shape of a sinkhole. Normally, sinkholes are created by the collapsing of a cavern roof, which takes the ground above with it. He noticed there was no water in this sinkhole, therefore he knew there had to be a drain nearby, most likely a cavern.
Knowing this, Amos began to search the edges for some opening to the possible cave system below. He found this opening on the lip of the sinkhole by noticing a small colony of camel crickets (which only live in damp, dark areas by nature) under a small ledge.
Upon digging out the first "room" of the caverns, he came into a large system of connected rooms, most of which were navigable and cleared from all obstructions. 90% of the caverns were naturally accessible and other than the entrance area, only 10% needed to be dug out. The use of scientific analysis makes the discovery of Skyline Caverns extremely unique.
However, the cavern floor was lined with approximately 14 inches of mud and clay, which had to be cleared before the caverns could be opened to the public on April 13, 1939.
The caverns are estimated to be approximately 50 to 60 million years old.
During the clearing of this mud, Amos and his men discovered another area in the caverns that had been blocked for many years, by a large amount of mud. Upon clearing the newly discovered area, the geologist discovered anthodites. Anthodites are an unusual form of crystal, or perfect 6-sided crystalline structures made of pure calcite. These crystals are protected by Virginia State Law, and are kept behind closed doors that a tour guide must open for the public to view them.
Today, guided tours (as opposed to self-guided tours) are given year-round, including on Christmas Day. Tours will depart every 15 to 20 minutes, lasting approximately one hour and cover about a mile and one-eighth of walking. This covers about twenty percent of the caverns. The remaining eighty percent is inaccessible to tourists.
A knowledgeable guide will lead you 260 feet below the Earth's surface. Cavern formations visible on the tour include stalactites, stalagmites, columns, "flow-stone", anthodites, and aragonites.
Skyline Caverns also features five flowing streams, three of which will be visible on the tour.