Boiler is 5-star! Visited Sunday afternoon - arrived around 3PM. Quite busy - mixed crowd, all ages. No rentb-ys (at least that I saw and I was there for several hours). By 6pm the place had at least a couple hundred guys in it. Amazing space. 3 floors. Enormous locker room (there must be 500 lockers if there's 1), showers, restrooms - all spotlessly clean. Large bar/cafe with external patio. Lowest level is vast with rooms, saunas, showers, maze, dark room(s), glory holes, video room, chill out area, you name it. This is a world class sauna. I'd compare to Phoenix in Koln. Hot! My only complaint (and this is purely personal opinion) is that the guys in Germany are not as attractive/hot as the guys in Spain. But without doubt this is THE sauna in Berlin.