Sorry to be the bearer of bad news. The only saunas in Germany are gay saunas. If you are thinking of Brazilian type saunas with rent boys being in Germany, it is not going to happen.
Your friend told you about saunas in other cities in Europe but omitted one sauna in Europe that is predominately a rent-boy sauna, which is in Zurich, not far from Germany. The name of the Zurich sauna is Paragonya wellness club - http://www.paragonya.ch/and https://www.youtube.com/watch?v=s2g0VcjgsK4
The sauna is in a very nice section (old) of Zurich, located in a commercial building. The sauna usually has more than 40 working guys. Considering that you like Brazil so much, you might like to know that a large portion of the working guys at the sauna are Brazilians.
The working guys are of a varied mix. Of course, most of the Brazilians are "butch" while the Asian working guys are usually "twinks" and are often rather feminine.
The club, itself, is extremely clean. The "rooms" that are available for getting together with working guys are rather flimsy with the door made of some sort of thin plastic. The use of the "rooms" is without cost.
Check out the web links I provided and you will see the general layout of the place.
Having been so many times to the Brazilian saunas and the sauna in Barcelona (thermas), I cannot recommend Paragonya as a place to make a special trip to see. It is okay but it is not one of my favorite saunas.