Meramec Caverns

"With a nickname like the “Cave State,” Missouri certainly isn’t short on impressive caverns. Of the more than 6,000 across the state, however, Meramac Caverns is the largest—and stays open year-round for tours. Said to have been a hideout for the outlaw Jesse James in the 1870s, the seven-level, 4.6-mile-long natural wonder was purchased by Lester Dill in 1933 and opened as a tourist attraction in 1935. Today, visitors can take guided tram tours past the cave’s complex mineral formations, stopping at a “wine room” (named for its grape-like botryoids and accessed by a long stairwell). While exploring, keep your eyes peeled for the resident tricolored bats that call Meramac home."