Grand View Park (also known as Turtle Hill) is not on the radar for most San Franciscans, but to residents of the Sunset district, it's a great workout spot. The stairs leading up to the hill are steep, and I often saw quite a few locals running up and down, Rocky-style. Once you get up to the top, the view - on a clear day, which is rare - is one of the best in SF. You get a fabulous view of both the ocean and the city, and the best part is that there are rarely any other people around to ruin the scenery with chatter. Be careful, though: it is often very windy, and can be a good deal colder than the surrounding area.