The main characters wake up in a cube, with a door on every side of the cube, and each door leads to a similar cube. Some cubes contain death traps, which kill you either instantly (Alderson), or slowly and painfully (Rennes). Every method of detecting traps seems to fail at some point, so for a large part of the movie, people are risking a high chance of death every time they enter a room in a desperate attempt to reach food, water, or help.
Further disturbing is the fact that the puzzle doesn't have a point: in a discussion, Worth implies that the puzzle isn't part of a grander scheme, that people are being stuck in it because "you either use it, or admit it's pointless". So basically, they (and who knows how many others before and after them) are in this situation because somebody built the cube and they want it used. That's it, that's the reason. "Because it's there." One tagline foreshadows this chillingly with "Don't Look For A Reason...Look For A Way Out."
You wake up in a room, surrounded by strangers who may want to kill you and hundreds of evil deathtraps. And if you don't escape fast, you'll starve to death.
The intense amount of claustrophobia that one would feel being stuck inside the cube. Even if one does not have claustrophobia, they will most likely develop it the longer they remain inside the cube. Combine that with the death traps and the hopeless futility of trying to find a way out and you are left with an insanely nightmarish situation that should only be reserved for the worst of the worst of nightmares.
Anyone who has some experience with abusers and/or people with VERY bad tempers knows how scary a man like Quentin is. He's obviously a sociopath gone over the edge. Not to mention the fact he's also an Ephebophile who clearly harbors intents to rape the young female prisoner. Quentin was a bigger monster than the Cube ever was.
