This is the cave author Mark Twain described in five of his books. The cave was first shown in 1886. It is a registered National Natural Landmark. This is one of a few labyrinth style caves in the world, where the passages form crisscross patterns. The tour lasts one hour. There are no stairs – good walking shoes are recommended. The temperature inside is 52 degrees Fahrenheit, year-round. Located on Route 79, two miles south of downtown Hannibal. Tickets: Adults, $18.95; ages 8-12, $9.95; younger than 8, $4. Group rates offered. Cameron Cave (tours by lantern light) and Cave Hollow West Winery are on-site.