Instead of dropping down from the high corner block, , turn left, take a running jump across the pool, and grab onto the climbable wall on the other side of the canyon.
Climb down the handholds until Lara is hanging just above the first horizontal crevice. Let go and quickly grab the crevice.
Climb down to the angled opening on the right.
Position Lara's hands at the top of the point and climb to the right as far as possible. Then drop and grab the edge of the opening below. Lara automatically shifts a little to the right in order to make the grab. Pull up into the cave with the secret.
- OR -
Or, continue climbing down the handholds until Lara is hanging just above the second horizontal crevice. Let go and quickly grab again. Then traverse along the crevice to the right. Pull up into the cave with the secret.