Seneca Caverns is renowned as "Ohio's Greatest Natural Underground Adventure." The caverns were discovered in 1872 and have been designated a Registered Ohio Natural Landmark. Just a short drive from Sandusky and Bellevue, visitors can take a one hour guided walking tour through the caverns 110 feet below ground level. The caverns are open Memorial Day through Labor Day seven days a week. Address: . Flat Rock OH USA 44828-0595 1 419 483-6711