I used to do work-study for the Landscape office in PP7, on the Disch-Faulk route. There were several tunnels over there one directly below the "greenhouse" where they keep the plants that decorate stages for speakers. There is also a huge compost heap on the north side of PP7 between the building and the fence, and there is a break in the middle of it for a grate with a fan like the one you describe in your story. I'm guessing there are a lot of tunnells on the part of campus east of 35.