Natural Tunnel State Park in Virginia’s Appalachian Mountains preserves the Natural Tunnel, a vast cave through Purchase Ridge that formed over more than a million years as acidic groundwater dissolved limestone and dolomite and Stock Creek cut underground through the rock. Up to 200 feet wide and 80 feet high, the tunnel is large enough to function as an active railroad passage, linking striking geology with more than a century of industrial use. Known long before the park’s creation, the site also contains fossils, local legend, and a long tourism history. Railroad traffic began here in the 1890s, and the park was established in 1967 and opened in 1971.