Indiscreet Stairway (1966)

She didn't know what going down was until she tried the...

The talking staircase in a French apartment building reveals the intimate lives of five of the building's tenants: two bikini-clad young women go swimming together; a muscleman who is pretending to be a painter uses a nude model; Marcy, a 15-year-old, skips school to attend a party with the milkman; and a woman whose husband is out of town showers and applies skin lotion before going to bed.