I used to work in some offices near the old Sears department store by I-71. One day a co-worker asked me if I wanted to go exploring. Apparently, two of the old subway tunnels---short tunnels through the hillsides---run along the eastern side of the highway (https://www.google.com/maps/@39.129868,-84.4952788,769m/data...). We parked on Oak (or was it Lincoln?) and walked down to the entrance in hip-waders and hardhats. If I remember it correctly, we ended up on the other side of Taft or McMillan (https://www.google.com/maps/@39.1256898,-84.4971403,140m/dat...). Not many signs of human habitation. One of the tunnels was pretty flooded. The other had what looked like the remains of a campfire, maybe a few bottles.