The gay center of San Francisco (and arguably the US), the Castro offers visitors great food, drinks and shopping, in addition to some of the hottest and best-dressed men anywhere!
If you're looking for a movie, be sure to check out the Castro Theater - a huge Spanish Colonial affair with a pipe organist before most showings.
Also nearby is Dolores Park, the Lower Haight - with Twin Peaks a fairly strenuous half hour hike up the hill (Kite Hill offers similar views with much less hiking).
Wikipedia: http://en.wikipedia.org/wiki/The_Castro,_San_Francisco,_California