And I've got yet another one: Martyrs
A french horror film made in 2008, Martyrs centers around two girls named Lucy and Anna. In the first scene of the film, a young Lucy escapes from a dark room where she has been held captive and tortured. What happens afterwards is all related to that experience but there are a few twists in the film. I can't really write anything else about the story because that would just ruin it.
I usually don't have trouble watching horror movies, but there are some scenes in this movie that are just gutwrenching to watch. It's not the kind of scary-thing-jumps-out-from-the-shadows fear that is so common in the genre, it's more angsty. You really feel sorry for the victims. I highly recommend this film, just be prepared.
10/10