NOTE: Only works in v1.0-1.1

Try to wedge yourself into the corner by looking at the torch and pressing back and right. Position your cursor so it's right in the middle of where the pieces of metal on the torch intersect. Then, while sprinting, press forward shortly followed by jump, in a swift motion. You should climb up.

Then crouch and work your way around the slightly protruding invisible wall and fall into the water.

Full catacombs early: