"FKK Sauna clubs have been part of the German landscape for over 25 years and can be found in or near most major towns and cities. These clubs offer discerning gentlemen a place to relax in a discreet, legal environment designed for their pleasure. They are similar to health spas or health clubs, where guests can have a massage or a sauna bath; enjoy catered, restaurant-quality food and beverages; and enjoy the company of attractive women, all at a reasonable price."

Thats the intro paragraph from the "FKK Club" Board here on TER.  It's under the TER General Boards.  I've never read it, but it will probably have the information you are looking for.