Oxford ♥♥♥ is probably less picturesque than Cambridge, but far surpasses the other in architectural grandeur.
The center of the town is bigger and, unfortunately, more touristy, but the Broad Street is very beautiful, and several towers, churches, colleges and other buildings all over town date from medieval times. Many church gardens house cafes, which in nice weather do not have spare tables.
Christ Church college has an expansive and serene quad and is also home to the town cathedral. The college is definitely worth a visit.
Carfax Tower is the best known high point that one can climb for a view of the town from above. There are several others.
For a lunch/snack, Frommer’s recommended an eatery on Broad Street, called Morton’s, but it turned out to be an unremarkable baguette-sandwich shop that served soup in foam cups, with an unappealing seating area in a courtyard behind. The Buttery, a few doors down the street, was considerably more pleasant, with better selection of sandwiches and other meals and street-side, as well as upper-floor, seating.