The SF Hilton (Union Sq. location) has a very good hotel gym. If you have HHonors status you get in for free. I don't know what the day rates are if you don't have status. The Fairmont is connected to a Club One - but the hotel location isn't great - it would probably "get the job done" but it is fairly rundown. I think if you are any status of the Fairmont program you get in for free.