Cure
25 years late to this, but woah.
I remember setting up the timer to record Ringu on Film4 when I was about 15 and then putting off watching it for about two weeks. Then my dad wanted to delete it from the recorder so I had to watch it and it scared the shit out of me. Glad I didn't know what Cure was because I would probably still be catatonic if I'd seen it then.
I'm struck by just how stark this is and how far it strays from established horror tropes while being one of the scariest movies I've ever seen, which makes sense because there's a big chunk of shared DNA with Spoorloos here. There's also something reminiscent of Prince Of Darkness too, with it's quiet apocalypse.