I was in Cologne for work and figured I'd visit a new  FKK. Samya was a very promising option, albeit the experience was not fantastic for a couple of reasons.  

Reason 1: they are in the middle of restructuring. Rather than closing the place for a few weeks, they rearranged things, but the net effect is that the locker rooms are in a corridor and every 30 seconds (or less) you need to squeeze to let other guys go by. Also, if you want to take a shower, you need to pass externally to the building, including a flight of emergency stairs. If it's raining, you'll need to walk a stretch in the rain. Anyway, this is transient. The problem will probably be gone by the time you get there (if you ever decide to).

Reason 2: "company culture": girls seem to have "unionized". 50 roses will get you nothing and there seem to be a general understanding that visitors should be upsold with any excuse. This is hard to notice for someone who has no experience with FKKs, but it was very noticeable to me.  

The first shot-in-the-dark encounter was with a curvy Turkish milf, who promised the world, but who performed mechanically in the room. I wasn't happy. The first 150 roses were gone. At that point, I became a lot more careful and interviewed a bunch of girls. The situation was always the same. It took no more than 3 or  4 questions to get them to remove their mask "do you want to fuck or not?" and then walk away. As a litmus test, I talked to a short, curvy, not particularly pretty girl with glasses. Her young age was the only thing that saved her. Believe it or not, she was unionized too.
I was tempted to go, but I kept looking at this Rumanian chick that went by the name of Kate. Tall, but not skinny. Long red hair. Honestly a 10 for the looks. As I feared, her performance was not stellar, but she was so beautiful that she was still worth the 200 roses I gave her in the end, We had agreed 150, but once in the room, she said that that was CBJ, another 50 was needed to remove the cover. I hated that, but I wasn't going to let 50 euros totally spoil the experience after all the efforts to be there. Anyway, LFK, BBBJ, DATY, Doggie.  

Anyway, if you don't have another option and you are visiting from the US, I guess that Samya is still a possibility, but not the best option by far in my opinion.