I’ve been to a number of sentou (public bath) and onsen (hot spring bath) all over Japan by now. In some of these (both sentou and onsen), I saw bathtubs labelled 電気風呂. I know enough Japanese kanji to read this as denki furo or electric bath but I do not know enough Japanese to understand what this is about (and arguably I might be reading it wrong and thus attempting to understand it wrong).
All the sources I could find by Googling are in Japanese and thus way above my level.
Surely a 電気風呂 isn’t a bath with an electric current going through it, but then what in the world is it?
Note: I have not been brave enough to just go inside and try it out.