The Cincinnati Subway is by far the most famous abandoned subway on the planet. It's also one of Cincinnati's most infamous landmarks, and aside from randomly scheduled and extremely expensive tours, no one ever gets to see it.
The subway was built by the City of Cincinnati between 1920 and 1925. Seven miles of the line were constructed in some way, from downtown Cincinnati beneath Central Parkway, and on up to Norwood. Construction was stopped in 1925 when the city ran out of money to continue. The project ran extremely over budget as a result of inflation. The bonds taken out to provide the funding for the project were taken in 1916, shortly before the US entered WWI. As a result of the war effort, construction was put on hold until 1920. By the end of the war, inflation had made the $6 million worth of bonds worth just a fraction of what they had been 4 years prior, and the budget for the project had more than doubled due to increased supply and labor costs. Currently, there's a little over two miles of tunnel that exist, and four underground stations. To read up about more of the history of the subway, visit Cincinnati Transit.
Below are photos of the remaining subway tunnels and stations, sorted by station from the northernmost to the southernmost.
Detail map of the Brighton Station. Brighton Station is the northernmost subway stop that was built, past this point a few more above ground stations were built at places like Ludlow Avenue, Clifton Avenue, etc. on the route up through Norwood. Brighton was my personal favorite station because it represented what would have otherwise been the standard station, had the rest of the system been built. The other stations all have their eccentricities: Race St. being the hub, Liberty St. being a bomb shelter, and Linn St. being nothing but a solid concrete wall. That said, my favorite photos came from Brighton.
Linn St. Station is the least exciting of all the stations, because it's been completely sealed over at the edge of the platform. I'm not sure why it was down, but it seemed as if Linn St. would have looked very similar to the Brighton Corner Station.
The Race St. Station is the largest station in the system, and would have been one of the main downtown hubs. It's the only station that has a central platform, and three tracks (the center track is a stub on either side).