To do this skip, follow these steps:

1. Jump repeatedly on the back of the cart when you go into the Red Hole.
2. Clip out of bounds and land close to the door where you use your first key.
3. Walk behind the big building until you find an opening.
4. Go through the opening and walk down the hallway.
5. Reach a loading barrier, wait for it, and then walk backward after loading.

Check out the video for a clear demonstration!