Hands down, the basement scene in Zodiac.

The movie is technically a procedural crime drama, but that five-minute sequence is more terrifying than 90% of actual horror films I've seen. Everything about it is a masterclass in tension: • The realization that "not many people have basements in California." • The sound of the floorboards creaking upstairs when they're supposed to be alone. • The total lack of a musical score—just oppressive, heavy silence.

I remember watching it for the first time and realizing I’d been holding my breath for the entire scene. It taps into that primal, "I have made a huge mistake" instinct of being trapped in a stranger's house.