While not the largest beach to visit, the Promenade is a nice place to take in some Vitamin D on a clear day. Lots of dogs wandering around, people strolling up and down, and warm, soft sand. Like everywhere in SF, it's hard to get into the frigid ocean waters, but it's a great place to take in the city and natural views. A little harder to get to by public transportation, but if you have a car, you can easily park in the lots near the Sports Basement.
Golden Gate Promenade, San Francisco, CA 94129, USA