Covering two city blocks on the Castro side of the Mission district, Dolores Park has more visitors per square foot than any park in the city. Tennis and basketball courts, pickup soccer, a children's playground (currently under re-construction), dogs aplenty, and expansive skyline views combine for a magically relaxing afternoon. It is delightful (and relatively safe) after dark as well. Bike polo is on (at least temporary) hiatus pending a political battle with the tennis players.
Regular park events include: the Hunky Jesus Contest, the Dyke March, various political rallies and large outdoor movie showings during the summer.
Bi-Rite serves up excellent ice cream and adjoins on the downhill corner of the park, while the Golden Fire Hydrant (which saved the west/south of San Francisco in the 1906 fire) watches from above... the gold is repainted annually :)
Wikipedia: http://en.wikipedia.org/wiki/Dolores_Park
