Go past the pool into the narrow canyon and follow the passageway at the end on the right.
Climb the stepped blocks upward and to the left.
Take a running jump across the first of 2 holes to grab the opposite edge.
Do not drop down, since there is barbed wire on the floor of the cave below. Instead, pull up.
Walk to the edge of the second hole and turn around.
Drop back and grab the edge, but before letting go, traverse a little to the right if necessary so Lara doesn't land in the barbed wire below on the left.