Shortcut #1, which is quite a bit easier, is shown here.
The screenshot above shows where you will be climbing. Lara is standing on the tall block from which you jump to grab the rope that opens the drawbridge. After opening the drawbridge as usual, swim across the pool and climb out of the water on the low ledge. Climb onto the next higher ledge. Turn around and jump to grab the next higher ledge, then the next. Now a huge brownish boulder blocks the way.
When you complete the level in the normal way, this boulder is dislodged by the rolling boulder from the interactive cut scene. After this, you can climb these ledges to get back and forth from the pool to the temple without any trouble.
In order to reach the temple now, you need to take a very tricky running jump (described below) past the boulder to grab the flat ledge above and behind it. After grabbing that ledge, pull up, turn left and take a running jump to the ruins. Climb the ladder on the left wall to reach the spot where you'd normally exit the ruins after the rolling boulder trap (CHECKPOINT 14 in the walkthrough).
You can do this before or after opening the drawbridge and diverting the waterfall; however, if you do it before, you will need to save at checkpoint 14, then reload and continue (or die and reload if you're playing a time trial). Otherwise, the temple interior is incomplete and you can't move on.
Now, the tricky jump. With the camera moved off to the side, you can see the ledge you want to grab just beyond the boulder. (It's labeled in the screenshot above.) However, you can't see the ledge from the position where you'll make the jump (shown below).
This is the approximate starting position for the jump. Note how the ledge comes to a slight point on the left side. Line Lara up as shown in the screenshot above, so her left foot is at the edge of the ledge, not quite all the way toward the back. Then run forward and jump off between the point and the front corner of the ledge. If you run at just the right angle, Lara will actually take off from a point slightly beyond the edge of the ledge, jump past the boulder without running into it, and grab the ledge beyond. Releasing Forward and continuing to hold Jump after takeoff seems to help, as does not trying to steer to the right in mid-air.
Various players have reported slightly different methods for this jump. Some have posted their own screenshots and gameplay videos showing their techniques. There are also a few different videos on YouTube, posted by stephietrl (here and here), delenne (here) and lolzz656 (here).
Once you make it, Lara will be hanging here. Pull up, turn left, and jump over to the ruins. Then climb the ladder 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 #1 | Return to the Ghana Walkthrough]