In 1940 the city sought the advice of several experts to settle once and for all the fate of the subway. The report recommended placing all streetcar and trolley transportation underground (i.e., a subway), but Cincinnati already had too many other expensive public projects underway. In any case, the plan was put on hold yet again when the United States entered World War II in 1941.[23]

Really good The Proper People episode where they explored this system. If you’re into Urbex I highly recommend.

Reminds me of fallout 3. And 4