My fave German language forum is roemerforum.com (most unbiased and entertaining)
Check my other, lengthier posts in this forum and those from others who've been there. I do not want to look like a spammer, so I do not repeat myself.
There are literally 1000s of them in Germany and each is different and independently owned and operated, very often by women who worked their way up in the biz.
The business models vary and so do the costs:
Entrance fees from Euro 20 - 100 (admission, locker keys, food, softdrinks, bathhouse amenities, robe, towels)
Session with a lady costs Euro 20->150, depending on services requested.
However there are also 'Pauschalclubs" who will charge a flat fee (~Eu 75~125) for a block of time (3-8 hrs) and one can use as many ladies as one can get hard for.
No they are not MP fishbowls, they are formatted after swing clubs and bathhouses. Everybody is NAKED (that's what 'FKK' means), you too.
The fees are set, no haggling or tipping.
Follow the links in
http://fkkguide.cyberfreehost.com , look at the pictures and read the texts. Too bad they do not really push for the tourist trade, so few offer English. Actually they cater mostly to the local clientele, often wealthy Benz/BMW/Porsche-driving businessmen who know the value of an Euro and prefer to operate economically. Not alcoholic pub crawlers or money wasting, party animal/gambling casino types.
Locations are usually remote from city centers and public transit.
Another reason why you'll need a guide.