SPOILER SPOILER SPOILER SPOILER
Okay, let me see if I remember how to do this. . .
Climb up the wooden ladder, shimmy across on the level below the ledge, and pull yourself up to the ledge (it's obvious by the placement of the ladders where I mean). Then go behind the funky looking block, and shove it forward, until you can't any longer.
Then go back around, get on the ladders again, climb up, and get on top of the block you just "popped" out of the wall. There is a ledge above the ladders you were just climbing. go to the opposite side of the block from that ledge, run and jump just at the edge and grab the ledge above. Pull yourself up, and this should get you on your way. If it isn't a running jump, it's just a standing one, I can't remember which.