On-sen...? [More mumbled to himself -- he can get the meaning from her words, even if he's not familiar with the vocabulary.]

Actually, you know-- I've seen a place that has something like this! I think it was some kind of luxury spa... except their baths are heated, of course.

I actually tried applying for an opening they had there for a night shift, but it was so hot inside, I almost passed out in the lobby...

[...admittedly, the fact that he was hardly eating anything at that point probably didn't help.]