... photo of a woman in a bathing suit.
It's not just the bathing suit. It's the woman.
ADDED: Try finding a bathing suit like that today. A search for "vintage one-piece bathing suit" got me to this pageful of tatters worn by mincing, wincing waifs. A search for "retro swimsuit" got me to this horror:
The suit for the out-and-proud anorexic.
Cartoon bones aside, the shape of the suit is all about rejecting a womanly body. I remember the time before the leg openings were cut way back to create the illusion that the hips and half of the ass were part of the legs. In the vintage photo, the region between the waist and legs is massive, valuable territory, owned and occupied by a woman of substance.