Inside the Lost Sea, America’s Largest Underground Lake and a Tennessee Must-Visit

The Lost Sea, America’s largest underground lake, is a natural wonder in Sweetwater, Tennessee, 50 miles southwest of Knoxville. - Located 140 feet below ground in Craighead Caverns, the lake spans over 4 acres with mapped submerged passages exceeding 13 acres.

- Visitors enjoy guided walking tours and electric boat rides across crystal-clear waters, home to large rainbow trout (fishing not allowed). - Rare anthodite crystal formations and Civil War-era saltpeter mining signatures are key historical highlights.

- Open year-round except Thanksgiving and Christmas; tours last 75 minutes; admission $28.95 adults, $18.95 children 4–12, free for ages 3 and under. The Lost Sea offers a unique blend of geology, history, and family-friendly adventure in the Smoky Mountain foothills.