140 Lost Sea Road, Sweetwater, Tennessee 423-337-6616 Enjoy a guided cavern tour that includes a fascinating glass-bottom boat ride on the Lost Sea, the largest underground lake in the United States. A U.S. Registered National Landmark, Lost Sea Caverns is open year round. It is located off I-75 between Knoxville and Chattanooga in Sweetwater, the “Southern Gateway to the Smokies.”
