A can't-miss visit for fire geeks, history buffs, and those who seeking to unlock the secret color-coding of SF fire hydrants (!!!) - the "San Francisco Fire Department Museum" packs an impressive amount of Victorian era firefighting equipment, relics, photographs and information into a relatively small firehouse (with an operating fire station adjoining)
The volunteer staff is friendly, helpful... and may let you "ride" an old fire engine for a photo or two, if you ask nicely :)
For walkers, the museum is 5 blocks from the Presidio and amazing hikes down to Baker Beach, the Golden Gate Bridge and/or the Marina District.
Address: 655 Presidio, SF
Website: http://guardiansofthecity.org/sffd/index.html