If you're having trouble with any of this, you may want to check out these awesome speedrun videos by Laraman and MMAN, both of which incorporate this shortcut.
The screenshot above shows where you will be climbing.
After opening the drawbridge as usual, turn around and jump to grab the dangling rope. If the mechanism rises up again, making the rope too high to reach, just climb the rocks and jump to grab the rope the way you did before.
Climb almost to the top of the rope and turn so the open drawbridge is on Lara's right.
Swing and jump forward to land on an invisible ledge, shown above. Carefully walk to the edge, near the tall rock formation on the right. As long as you inch forward gradually Lara won't fall. If you see her lurch forward, the way she does at a visible edge, stop moving to avoid sliding off. Jump to the flat ledge between the two rounded rock formations.
Turn left and jump onto the rounded rock beside the flat ledge.
This jump is a little tricky. Aim for the right side of the rock, as shown above. Try not to slide off the edge, but if you do, run around to the other side of the island and climb up to the rope again.
Once Lara is on top of the rounded rock, turn around to face the taller rock formation. Very carefully inch forward and to the right until Lara is standing on the tallest part of the rounded rock. This is actually an invisible protrusion above the rock (shown above).
Jump from here to the taller rock formation. Aim for the flat, lighter green area at the middle right, as shown above. Move to the top left side of the taller rock. Again, the actual surface of the rock doesn't match the visual outlines, so until you learn where the edges are, move forward gradually so Lara doesn't fall.
Jump from the top of this rock to the front left corner of the ledge in front of the ruins. Then go around behind the tall columns to the right.
Cross the dark area between the ledges. It's safe to climb down, or you can just cross the ledge with the square column near the wall. Jump onto the ledge on the other side and run through the fallen column.
Go around to the right to find silver reward #3 if you're interested. Then climb the ladder on the far wall to the ledge above.
This is where you'd normally exit the ruins after the rolling boulder trap. Pick up the main walkthrough there.
NOTE: CHECKPOINT 15, at this exit from the ruins, does not register when you approach from this side. So move carefully as you continue across the poles and ledges on the front of the ruins. Or, enter the ruins here, proceed to the checkpoint near the blade traps and then return through the hallway. You will have to outrun the rolling boulder, but when you emerge, checkpoint 14 will work.
[Shortcut #2 | Return to the Ghana Walkthrough]