Mark Twain Cave — originally McDowell's Cave — is a show cave located near Hannibal, Missouri. It was named for author Mark Twain whose real name was Samuel Langhorne Clemens. Clemens lived in Hannibal from 1839 to 1853, age 4 to 17. It is the oldest operating show cave in the state, giving tours continuously since 1886. Along with nearby Cameron Cave, it became a registered National Natural Landmark in 1972, with a citation reading "Exceptionally good examples of the maze type of cavern development." The cave — as "McDougal's Cave" — plays an important role in the novel The Adventures of Tom Sawyer (1876) by Mark Twain and was renamed in honor of the author in 1880.
39° 41' 19" N , 91° 19' 54" W