Hidden, SE11 5EQ
Hidden (formerly Studio 33) is a nightclub just off Albert Embankment, and not actually very well hidden, at that.
The bouncers are straightforward, although there's a no-chewing-gum policy in the club, and they'll confiscate any they find. Inside, the club (capacity 643 according to the website) is split into three main rooms, joined by a warren of wide passageways and staircases. This can make the club feel very crowded, with people pushing past all the time; on the other hand, it's quite conducive to wandering around and socialising; the layout reminded me quite a lot of Egg in King's Cross.
The main dance areas are smallish, but that doesn't seem to detract much; they've also had very good projection/VJ setups any time I've been there. The soundsystem in the main room was annoyingly muffled when we visited in March 2008, although it sporadically got better, as if they were having trouble with one of the amps cutting out. There are toilet attendants, but they seemed fairly unobtrusive; bar staff are friendly and efficient.
There's an outside garden/smoking area, which has a covered section with seats and heaters, and also a small stall selling chips (£2), burgers, and hotdogs throughout the night. Cloakroom charges £2 per item; water is £2.50, and they sell Shark instead of Red Bull, for £3 a can. You probably want to avoid the red wine.
Nearest cash machine is at the petrol station next door. There seemed to be a cash machine inside the club, but it wasn't working.