Even if you didn't go to an Ivy League school, walking around the campus is always nice because the campuses are so collegiate feeling and well kept. Neither me nor my partner went to Princeton, but when we were close, we definitely wanted to see what the campus looked like. The chapel is especially beautiful, with lots of ivy growing on all the buildings (I guess that is where they get the name from haha). The chapel is open to the public when mass is not in service. Wandering around is a great way to kill a few hours if you are in the area.