Sasha MOW
During the day this loft is taken by artists at work. At night, check their website to see what’s on - they have three floors mostly housing famous electro musicians. The club is not that big for SF but its gigs are quite crowded. Gigs are usually not free but sometimes you can put your name on a guest list following a link on their website - just come by specific time. It's a common practice for SF clubs - usually it's before 10 or 11 pm or later if you were put in by one of your DJ friends (it depends on the venue).
