After opening the exit door halfway, as described in part 3, go to the back left corner of the room (i.e., left when facing the exit, right when facing the entrance). Climb into the alcove and jump to grab the vertical chain.
Climb the chain and jump to grab the handhold ahead. (Here it may help to move the camera behind Lara and then jump forward.) Traverse around the corner to the right.
Jump to grab the ledge above and jump again to pull up.
Jump straight up to grab the horizontal chain. Climb hand over hand along the chain and drop down on the ledge at the other end.
Turn to face out over the room and walk off the edge to drop and hang. Let go and grab the handhold below. Again, traverse to the right. Jump to grab the horizontal pole. Swing around and jump to the ledge near the exit. This is CHECKPOINT 13.
NOTE: If you're playing the demo version, exit here to finish the level.
[Part 3 | Part 5 | Return to the Bolivia Walkthrough]