I’m Japanese and live in Japan but I’m one of those very very unusual people (I don’t know many others) that have no interest in taking hot baths, either at home or at “onsen” resorts. In fact, I do not have a bath tub at home (I do have a very nice shower room), by preference, totally my doing, a choice I made when I renovated my apartment, as opposed to living in an apartment with a shared bath or one w/o whereby people go to communal bath on a daily basis.
Anyway, Budapest is known for its natural hot springs (which I read they are not “hot” by Japanese standard) and it appears people have been going to hot spring baths and pools for a long time that are what we would call “spas”.
Since we were not interested in actually taking a bath or going to a spa, we never got to see inside of this enormous establishment Széchenyi gyógyfürdo in the Városliget near the Hősök tere.