Not just Brazilian rent boys, also -and especially nowadays- from the new european East, and these I find dangerous, or in any case I don't feel safe during a date with them anymore. Be very careful, they might be fabulous and nice guys, I am not saying anything against foreigners, but their survival instincts and learnt behaviours from their home regions, is not someting you will be able to handle by the time (or if) you loose control of the situation. Keep in mind they have barely anything loose, and you probably do. Even if the 'date' (in here or outside) goes well, you may be dissappointed when suddenly agreed practices are no longer in the deal and it's too late to back off and it's blamed on a misunderstanding (either your misunderstanding, or your language barrier's fault; it will never be their fault, though).
You get one for much less than €50 both in here and on the Puerta del Sol (same type of crowd, though). So if you're into bored thugs and dirty rat type of rentboys, you may as well go to the Puerta del Sol at night, at least you're in the open and on relatively neutral ground (unlike in the Adan sauna).
The entry above says "If you have any problem with the Boys tell it to the Staff". My view: don't rely on that 'backup', there is nothing of the kind. I have stopped going to this place not just because of the 'lord of the flies' type of jungle some boys turn this into (&dangerous for you), because because the Staff was actually conquered, frightened, desperate and powerless.
Kind of place: yes a Sauna, but a rentboy Sauna and not just ocasionally, but nonstop and for many years and decades now.
how big: quite big, on 2 or even 3 floors (it won't matter or make a difference), but empty and you WILL be approached by demanding boys and they will keep insisting.
what kind of people: You won't find a genuine local (spanish) hustler in here perhaps one or two southamerican boys (i.e. speaking spanish if that's a value-add for you), but these (including most Brazilian) can only be found on the Internet now.
what music: the telly is on and that's what you are going to be hearing as background 'music'.
cheap or expensive: entry ticket is expensive given the fact that you are paying for a cesspit and
best days/times to go here: anytime, there are 'resident' hustlers as the ones I have described.
If you happen to travel check the places listed in planetromeo (under 'guide', 'detailed Guide search' and then with criteria 'escort services') plus the Paragonya in Zürich and the Hühnerfranz in Cologne which are not listed.