In the evening, the Red Light District is full of tourists, gawking at the girls in nothing but skimpy underwear, beckoning men as they walk by. Aggressive girls will open their glowing doors and shout at you to come have a look. One girl even grabbed me by the shirt sleeve.
After midnight, the crowds thin out and what's left are the ultra-drunk groups of men (there are pretty wasted women in the mix- Girl after taking a shot of something from a little white cup: "Wooo! Let's go! That was a good shot" She stumbles a bit. Guy friend: "Heh heh, are you okay?" with general concern for her ability to walk across the canal bridge) who walk up and down salivating. Often there's one guy who's singled out from the group who everyone else is determined to get laid. I watched as they held one guy up to a lamp post and looked him in the eye, pumping him up, trying to convince him. The guy was so drunk I don't think he could have had sex with himself. They soon gave up and he stumbled behind (apparently he was up for a live sex show but they ignored his request). The other scene is watching one guy go in for 'service' as his buddies wait outside. After about five minutes, they grow impatient and leave. If they do stick around, loud cheers erupt as their hero emerges.
After midnight, the streets also fill up with drug dealers. They flank you on both sides of the street, seemingly choosing targets. As you walk by you'll hear them whisper "cocaine", "smoke", "ecstasy", etc. Shake your head and keep walking. Late at night when there are only drunks and dealers left on the streets, you get a bit paranoid with people following you down dark alleys.
Notes: If you do decide that you need the services of a prostitute, here are the basics based on my observation and survey work. You walk the streets and find someone desirable. There are girls of all types. Skinny, fat, young, old, dark, light, fake, real. Walk right up to the door and ask for prices. For a dreamy girl that you only see in pornos, 50 Euros will get you S or F. You pay first. The woman will take you into a private room (some rooms open onto the street so a privacy curtain will be pulled closed) and take care of you. There is usually no touching. If you want to touch, it's another 50 Euros and then you're welcome to do what you like. (Hygiene: They provide protection, a sink, and paper towels. But the surfaces used for the transaction are not changed afterwards. A handy towel is placed on the bed and helpful black lights may be used to spot, spots.)