Hotel of Free Love (1974)

Madame Robert makes ends meet by running a boarding house, as her colonel widow's pension is not enough. A Norwegian pensioner, being young and athletic, starts doing gymnastics in the nude, in plain view of all respectable guests. Instead of being horrified, that leads everyone to express their inner selfs, as well as outer skin. Madame Robert can't take this, and expels all the guests, save the young Norwegian man, whom she considers a pure youth who didn't intend to start an orgy. Soon, she falls to his manly charms, and then invites back her lodgers to make the boarding house more pleasant, or rather, a "hotel de plaisir".