There's a small reactor about 4 floors underground along engineering row at NC State. Most of the engineering faculty / programs moved to Centennial Campus a while back, but no one wanted to have to move the reactor.
Not only was there one at Ohio State, over across the river from the main campus, but there was a flippin' sign for it out on main road tell you which building it was in.
When I was in the Level 2 Anti-Terrorism course with the OHARNG we all had to bring in a photo of something around town we thought might be a security risk and explain why. I didn't have to think twice, and I didn't bother to explain why when I put the picture up.
This is a newer sign, but it's the same building