Hubbard's Cave, a fifty-acre natural area in Warren County, Tennessee, combines major ecological importance with evidence of long human use. The cave, entered through three openings at the base of a large sinkhole in a mesic oak-hickory forest, is Tennessee's largest gray bat hibernaculum, sheltering more than five hundred thousand gray bats along with endangered Indiana bats and five other bat species. Its entrances have been gated to protect hibernating bats from disturbance. Deep inside, preserved cane torch fragments carbon dated to about two thousand years ago show prehistoric activity, while the west passage also retains artifacts, signatures, and other remains from Civil War saltpeter mining for gunpowder.