oxford, cambridge, durham, bath, york (not so much the campus but the area in general), edinburgh, glasgow, queens, sussex, aberdeen. and no i don't go to any of those!
i have been to royal holloway on an open day. it does remind me of hogwarts. and you can stay in the founder's building which i thought was pretty awesome.
My list of beautiful unis
UCL (main building)
basically all the ivies (apart from princeton, they all look simple, yet beautiful. art of simplicity, perhaps?) and most liberal arts colleges in massachussetts
Stanford (in unique way)
University of Toronto (in particular, trinity college, university college, victoria college, st.michael's college)
University of Sydney