A small but genuinely curious attraction on the grounds of the Hamilton County Courthouse area. The monument commemorates John Cleves Symmes Jr. (1780–1829), an American army officer who devoted much of his life to the theory that the Earth is hollow and contains habitable inner worlds accessible through openings at the poles. The stone monument is topped with a hollow sphere — a literal representation of his beliefs.
Symmes was not a crank by the standards of his era; hollow-earth theories had serious scientific proponents in the early 19th century. He gave lectures across the United States and gathered genuine followers. The monument is a rare example of a city honoring a resident whose big idea turned out to be completely wrong, and all the more charming for it.