Move to the next level through the slit. To get there, switch from walking-falling 3D-state to a wall-sliding 2D-modus. Beware - this is not polished ;)
Tools and Technologies:
SharpDX Toolkit and some rendering code from an older project.
Should work out-of-the-box. I hope.
Make sure .Net is not forbidden.
Thanks to Andreas for matrix-fixing.