claustrophobic tension

A submarine with a leak in Das Boot. A cabin in a blizzard with seven strangers and one liar in The Hateful Eight. A jury room in 12 Angry Men where nobody leaves until they agree. The room is the pressure, and the film spends its runtime making it smaller.

The walls do the work. The space is too small, the people are too many, and none of it has anywhere to go. Whatever is outside has stopped mattering by the second act.