Twin Peaks are two hills near the geographic center of San Francisco, rising to 925 feet and offering what may be the best 360-degree panorama in the city. On a clear day you can see from the Marin Headlands to the south Bay, with the downtown skyline, the bridges, and the Pacific all spread out below you.
The viewpoint at Christmas Tree Point, just below the north peak, is where most people stop. It is accessible by car or by hiking up from the 37 Corbett Muni line. Go at sunset for the best light, but bring a jacket -- it is almost always windy up here, and the fog can roll in fast. Unlike Twin Peaks' more famous cousin Bernal Hill, tour buses do make it up here, so early morning or weekday visits are quieter.