There are walking trails all around them Trenton Grounds for Sculpture. About 15-20 min from Princeton. A beautiful and huge garden featuring large works of sculpture and a couple of very good restaurants. Washington Crossing State Park on the Delaware River is 20-25 min away by car. It can be combined with visits to the two touristy towns of Lambertville and New Hope.
New Hope is the weirder one.
Lambertville specializes in overpriced antiques. Southern New Jersey, especially the Pine Barrens. Delaware Water Gap and the Poconos Mountains. The Poconos are a popular ski area, and hence a bit touristy. Trenton farmers' market.