Posting pics or vids from sauna centers is indeed an invasion of privacy. Cause you're not in a public place.
Nude beaches are a different story, cause in public.
That being said, beneath is a link to a Dutch short movie about a boy going to the sauna with his parents for the 1st time. It paints a pretty realistic image what actually goes on in a public sauna.
https://www.reseau-naturiste.org/vid...?language_id=1