2) Brothels. There are brothels all over town. Check the papers or web. As many on this site have already discovered, Kamilla La Dee (www.kamilla-dee.com) is very good. Check out their web site for info and directions. The nearest train stop, if I remember correctly, is Blissestrasse, and from there you will have to walk a couple blocks. Use google maps or your smart phone. Or take a cab. Kamilla la Dee is in a pretty standard-looking apartment/house building. The door is near the corner of the building. Ring the buzzer, they'll buzz you in, go upstairs (or if you are confused and linger someone will come down to help). Like most brothels in Germany, a hausmädchen (not necessarily the 'madame') will take you to a waiting room and ask whether there was a particular person you wanted to see. If you called ahead and made arrangements, say so. If not, available girls will come in one by one. Then the hausmädchen will come back and ask which you liked best. That girl will come back and you will go off to a room. Most decent brothel waiting rooms have hidden cameras, and the girls will check you out first. So try not to pick your nose or scratch your crotch incessantly while waiting. If you do, you'll see only the most desperate girls.
Kamilla la Dee seems to be very professional and treats the girls well. As a result, the women there are pretty good; they're into what they're doing. Don't ignore the women whose photos are not shown on the website. They maybe have reasons for not showing their photos, but it is not because they are ugly. A girl there told me that the best girls don't show their photos, and maybe that's true. I've been with two women from Kamilla la Dee who don't have their photos up, and they were great. One was a relatively convincing nymphomaniac; if you are into juice and loud vocalization she will make you happy. Another is incredibly sweet. I would marry her.
3) Escorts. There are loads of agencies with escorts in Berlin. Or check the Berlin Craigslist ads ('Dienstleistungen...Erotik). English speakers: Don't be put off by Craigslist in German. Most of the ads are in English. Berlin is easy for English speakers. Craigslist providers tend to be semi-amateurs and short timers, and the prices tend to be cheaper than through an agency. A friend of mine (an American college student on a lark) works through both craigslist and an agency. Same girl, same service, but the Craigslist prices are a lot cheaper. Why? No overhead. Agency owners charge a lot (25-50%) for a web site and answering the phone. Most of this particular friend's work comes through Craigslist. Plenty of rich international businessmen use Craigslist, so you won't necessarily be slumming by looking for a bargain there. But you will be gambling a bit with the professionalism. Agencies usually only hire reasonably reliable good looking girls.
4) Street girls. There are street girls all over Berlin, especially in the summer, but year 'round there are two main places: Kurfürstenstrasse (Not to be confused with Kurfürstendamm, or Ku'damm), and Oranienburgerstrasse. Kurfürstenstrasse will have girls out pretty much all day, at least in the afternoons and into evening. A lot of them are Eastern European. They are cheap; you can easily get everything for 50 euros. But the girl will probably look a little on the edge and smell a bit fishy. Kurfürsten is sad, and a good place to risk an STD. But you will get a cheap hole for your dick, if that's what you're after. if you need one, the girls can take you to a room nearby, maybe in the back of a bar. You will likely have to pay for the room yourself, but it will only be maybe 10 euros.
Oranienburger strasse is an increasingly touristy street with lots of bars and restaurants. Oranienburger used to represent edgy East Berlin, but now it's bordering on cheesy, at least in the summer when there are too many pub crawls and drunken tourists. From 9 PM until about 5AM, the street is filled with girls in hot pants, stockings, and corsets (this is standard Oranienburger uniform -- very recognizable). If you make eye contact at all, they will ask where you are going and pretty soon whether you want to have fun with them. Almost all speak pretty good English, and many some other languages. All are German girls. Standard cost is 80 euros for half an hour, which includes 'hand job and blow job'. They will take you to a set of rooms and offer you a free drink. Don't worry about where they take you; it will be relatively close and everything is safe. But once you are there they will try to escalate the prices. Getting their shirt off will cost you more money, and you will never get their stockings/underwear off. Blow jobs are usually faked. Oranienburger girls are mostly a rip-off service for drunk tourists. I would feel guilty writing that, because some of those girls are friends and I helped train them, but I am pretty sure their usual customer base (drunk English lads or 50+ confused tourists) don't read this site anyway. So I doubt this will hurt their business. If you want to do the Oranienburger girls a favor and make me feel better about dissing them here, talk to a bunch, see who you like, and take one for a drink instead of to their room. They'll happily have a drink with you, and a lot of them are lots of fun. The bartenders around there know the girls and you have nothing to be embarrassed about. Try to avoid the Gold Club, though. Or if you do go in there, ask for a drink menu and check the prices before you pay. Don't be ashamed to speak up if you're getting ripped off. In fact, they'll probably respect you for not being an idiot. Some of the girls on Oranienburger also do escort work, so if you really hit it off with someone you can possibly arrange a better date for another day.
Disclaimer: I obviously know the Berlin prostitution scene pretty well, and have friends in the business there. However, everything above is my honest advice, from one guy to another. I have shilled for girls before, but only when I felt they honestly deserved the praise, and never on this site. Con artists have no place in any business, including prostitution.
Enjoy Berlin!