NOTE: Only works in v1.0-1.1

Find the piece of rubble on the ground that I point at. Stand on top of it, then inch yourself left until you're through the wall. Keep inching until you can see the rock through the other side. Try to position your mouse to look at the black smudge in the top-middle of the rock. Then, hold forward, followed shortly by jump. (The timing is slightly different than the first OoB setup, you'll want a smidge more speed.) Don't forget, you need to hold forward and jump in order to climb up, but stop holding them once you're sure you're climbing, otherwise you might fall back off.

You should now be on "top" of the rock, but not quite the tippy top. We're sort of inside the rock, but can still climb up to the top with some repositioning. First, hold right until you're fully against the brick wall. Then, jump and press forward (in that order) and you should climb up to the tippy top of the rock. (If you press forward first, you'll fall into the rock and get stuck. There's a rock to the left you can climb up which should get you out.)

Then just jump towards the brick ceiling and you should climb up.

Full catacombs early: