The Cincinnati Subway is a set of unused tunnels and stations for a rapid transit system beneath the streets of Cincinnati, Ohio. It is the site of the largest abandoned subway tunnel in the United States.

• Rapid Transit was seen as the solution for downtown congestion during the first quarter of the twentieth century. Six million dollars were allocated for the project, but construction was delayed due to World War I. Unexpected post-war inflation doubled the cost of construction, so the project could not be finished at the original estimated price. Despite various attempts to use the subway tunnels for mass transit, thus far all attempts have been unsuccessful. Political squabbling, The Great Depression, World War II, and the rise in popularity of the automobile have all contributed to the current failure of the subway.