I've pressed literally every button I have to get past that wall. I've waited, I've looked back, I've walked back, I've tried looking for doors, holes in the floor, holes in the ceiling, switches, and I just can't figure it out.
I guess whoever rated it got stuck, too.
I thought this might be a demo with some of the scenarios excluded, but it looks like at least seven are included based on the game files.
I will say in roughly an hour of trying to figure out the wall, I found a couple of cool ways to break the game. If you walk straight back from the beginning, you can walk up the debris pile and straight out of the level.
Also, I figured out why the fog area moves you back to the center of the tunnel if you're at the sides. There's an invisible "door" that works as the access point to the fog area and the trigger for death. It assumes if it renders the door, you've looked back, but it also renders the door if you walk backward through it, which also causes death. Same scenario for the crusher wall. If you walk backward far enough once you enter the wall area, you "see" the wall trigger, and you'll be crushed the next time you walk into its area of effect.
Another funny thing: after you exit the fog area (but before the wall) you can look back all you want, but you will die instantly as soon as you walk into the fog area again, no matter which direction you're facing. If you go in facing the "wrong" way, though, you'll start coughing before the fog even manages to appear.