Another disturbing thing about the ending *spoilers*
The film wasn't too subtle with the sexual tension between the teacher and Sid. While the camera was zooming in on the kidnappers preserved heart in the jar, you can hear the two of them having a conversation about heading off to do something together, perhaps some "extracurricular activities"?
The ending of Fortress was a complete game-changer, a total departure in the movie's initial tone. At first you're rooting for the kids and the teacher, and when the credits roll, you think "Wow....these are some messed up people!"