Oh I can assure you, millions people in the northern europe do exactly this ;)

EDIT: I guess it depends on your definition of "humid". But 90C and regular water infusions are pretty common sauna conditions.

I guess I am a revenant - I get into one regularly in my basement.

Haha no, I been in 90c saunas many times. Can I stay there for a long time? Heck no. But some people can and it doesn’t kill you (maybe if you have some preexisting condition)