Go to the beach! Many of the beaches have nice boardwalks, though you will find homeless people so avoid if that makes you uncomfortable. In college we would walk down to Black's Beach in La Jolla (the semi-official nude beach, which is right below campus).
Actually walking around UC, San Diego is really, really nice at night. Just a warning as part of the Stuart Art Collection (stuartcollection.ucsd.edu), the trees talk and sing. It's creepy at night.