Heh, Berlin came to mind for me as soon as I saw the thread title... I didn't know "Barelin", just managed to experience it 10 years back. Yep, it's all true. The gay district has more coffee shops and leather stores than you can imagine. There's baths and erotic mazes and everything else you'd want. And it's all safe and orderly (the streets I mean). London for example is NOT the same, SoHo there is full of scammers and worse.
I stayed near Nollendorfplatz U-Bahn station which is very close to the major gay village and has extremely easy access to anywhere in the city. But there's other areas that are just as good, if you look into it. (Nollendorfplatz is close to the city center of old West Berlin and so it is a built up, expensive commercial area.)
Back when I was there the mobile apps weren't a thing, I would have got way more ass than I already did if they were... I think the US apps will work there just as well, or just go to one of the baths and ask your trick what he uses