OK, you're not suppose to take pictures at the red light district, but Ana's friend did (this isn't from my trip, but I put it up so everyone can see). This was taken away from the main strip but the has a similar setup. The doors reveal the girl and the room. If a guy (or girl perhaps) is interested, they open up and go in. If the curtain is drawn over the door, that means the girl isn't there or is "occupied". The main strip has more doors in a row and is spaced much closer. Also, there is generally a red flourescent light over head each door.