Woman in the Dunes

Woman in the Dunes (Japanese 砂の女 Suna no onna), also called Sand Woman and (The) Woman of the Dunes, is a Japanese film released in 1964.

Niki Jumpei was an entomologist (a scientist who studies insects for those of you who have not brushed up on Greek-derived words). He was simply just trying to collect insects that inhabit sand dunes on an expedition. Since he missed the last bus, the villagers offer him to stay the night. They guide him down a rope ladder to a house in a sand quarry where a young widow lives alone. The villagers employ her to dig sand for sale and to save the house from burial in the advancing sand. Unfortunately, Jumpei discovers the next morning that the villagers don't want him to leave and they want him to help the widow in her endless task of digging sand. Jumpei must find a way to deal with this situation.

Tropes used in Woman in the Dunes include:

Bittersweet Ending: The good news is that Jumpei found a way to improve life in the pit by drawing water from the damp sand at night. The bad news is that he has gone missing for 7 years, and it's hard to say what would happen if they find him.
No Name Given: The woman doesn't have a name.
Stockholm Syndrome: Jumpei tries to escape a few times and fails. Eventually, he gets so used to his situation that he decides not to escape when the opportunity presented itself.
Town with a Dark Secret: Well, considering that this village is forcing an outsider to dig sand, a job that is not fun or constructive by any stretch, the village may qualify for this trope.