I've done Berlin a few times.  I keep coming back to Airport Girls, which, when compared to the FKKs in Frankfurt and other parts of Germany, is definitely on the lower end of the scale.  But, it's a "partytreff" flat-rate place, so it's a good place to do consensual adult things without busting the budget.  There are other gangbang places such as Annie Porsche and EW.  I've not been too successful at them.  There are usually only 1-2 women and what appears to be a bunch of local "regulars".  I've heard good things about the Insomnia Club.  On certain nights, they target single guys and bring in professionals to make sure everyone is properly taken care of.  You may also find yourself in a group setting with amateurs as well.  I've never been able to attend, because things happen long after my 63-year old bed time.  Then, there's Artemis.  I've done numerous FKKs in Germany and Austria so I wasn't attracted to Artemis.  If you've never been to an FKK or have only been once, you can't go wrong.  There is also the famous "stroll" on Kurfürstenstrasse.  It's completely unbelievable!  I have never partaken because of the attendant risks.  But, it's an interesting experience to simply go there and walk around for a while.  I've never done the escort scene in Europe.  There are so m any different things you can do in Europe that just aren't available back home.