Windows 7/Chrome 4.1
Reproducible
I was bouncing around "The Entrance" and took a leap towards the "Level 1 West" Signpost. I managed to slip through the ramp up to the "Ilmenskie" Signpost and the wall behind the "Level 1 West" Signpost.
Was able to escape the pit of doom by leaping up and hitting the "Level 1 West" Signpost.