Originally Posted by
satori
Hearst Parking Garage offers 24 hour parking for $20 per night, but no in-out privileges. Hearst Garage is accessed from Third Street directly across from the Westin Market Street. It is a four block walk (ten minutes) to the Grand Hyatt. I use this parking garage regularly when I stay at Union Square hotels.
http://www.hearstbuildingsf.com/garage.htm
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Beware!
There is a nearby parking lot just south of Hearst (completely different side street) that can be much more expensive. There is a reasonable daily rate, but it is not 24 hours; instead you have to be out by some ungodly early hour (well, ungodly for me). Be sure you choose the Hearst garage -- accept no substitutes!