Follow the bank downstream to the rock ledge at the first corner.
Take a running jump from this ledge to the corner ledge on the other side of the stream.
This ledge doesn't quite extend around the corner, but a bit of it sticks out. Take a running jump from the protruding edge of this ledge to the next ledge downstream.
Walk to the far edge and take a standing jump with Action to land on the small, square ledge between the two waterfalls.
Turn left and take a carefully angled running jump past the center pillar...
...to land on the ledge on the left just beyond the waterfall.
Turn around, walk to the edge, and take a standing jump forward to grab the climbable wall next to the waterfall.
Climb down to the middle of the rock ladder. Try to position Lara a little above the ledge behind her.
If you look closely, you'll notice the seams in the wall textures. You want to position Lara's feet on or just below the seam at the same level as the ledge behind her.
Then press Jump to backflip onto the ledge. Turn around and move to the other end of the ledge.
Stand at the outer corner, angle Lara toward the climbable wall, and jump forward to grab it.
Climb up into the TNT CAVE.