Lost River Cave in Bowling Green, Kentucky, is a seven-mile cave system built around a river that briefly appears above ground before entering the cavern through one of the largest natural cave entrances in the eastern United States. Formed in Mississippian chert and limestone, it is also an important archaeological site with evidence of human presence reaching back about 10,000 years. Over time, the cave and valley served as a source of waterpower for mills, saw military use during the Civil War, and housed the Cavern Nite Club from 1934 to 1962. After severe decline, restoration begun in 1990 returned it to public use as a protected landscape and show cave.