Spoilers if you haven't seen the movie yet...
The entire movie is the main characters trying to escape the hospital as the ghosts that resided in the psychiatric hospital attack and haunt them, the building itself is shown to constantly warp time and space, for example - many scenes include when the characters go back to the exit of the door they came in since the beginning of the movie, only to find another hallway, random doors and objects appear out of nowhere, and throughout the film is always portrayed as nighttime as their camera's clock goes haywire.
Thoughts?