Fourth side room with toxic water/ Getting the Treasure (27/30)
Use the Grapple to catch the metal ring above. Drop off the ledge and climb down the grapple line.
Now wall run and jump to grab the handhold on the right wall. Release to grab the lower handhold.
Jump twice on the right to reach the handhold in the corner.
From there, jump to the right to grab the edge of the alcove. This is a long drop down and Lara will grab the edge with one hand. Press the Interact button to save her and prevent her from falling into the toxic pool. Pull up and pick up the Treasure (27/30).