Woman in the Dunes (1964)

Woman in the Dunes (1964) is very, very sandy. In fact, it's so sandy that the crux of the entire plot is about the commodity in the little desert town in Japan. Eiji Okuda plays an entomologist there to collect sand insects, not so much for work but as an escape. When he misses the last bus into town, the locals encourage him to stay in a shack where a woman lives - but to get him there, they have to drop him down into a pit surrounded by - you guessed it - sand. Once down there, the woman explains that they are stuck forever, as the locals would have to physically pull them out for them to be able to scale the sliding dune walls. Instead, they are left there to shovel falling sand out of the house so that the locals can sell it for construction. And what is there to do when one man and one woman are left with nothing to do but shovel? They have sex! We get to see Eiji's butt when his new lady friend bathes him. The woman in the dunes is one lucky lady!