With the opening from where you entered this area to your back, turn left and jump to grab the wooden beam jutting from the wall.

Pull up and walk towards the wall. Jump up to grab the handhold on the wall and climb to the next one on the right. Jump to grab the next handhold on the right and...

... traverse around the corner. Grab the ladder, but do not climb up. Instead, drop into the pool below.

Alternatively, after returning to the column from the last Treasure, drop to the ground and go to the left (if the opening you came from is behind you). Jump into the water and swim to the right and through the tunnel. (You walked in this tunnel earlier).

Swim to the other side and climb on the wooden beam. As before, perform the Chimney Jump...

... to grab the horizontal pole above.

Climb on it and jump forward. Quickly throw the Grapple to catch the metal ring above.

This time, climb up the cable line until Lara's legs are lined with the ledge on the right. Wall run to this ledge and break the vase to find a Treasure (24/28).

Hang from the edge of the doorway and drop down. Draw weapons and kill the giant spider that attacks.

Go to the other side of the room and climb up the shorter vertical column. Perch on it and jump to grab the ledge ahead. Pull up and pick up the Treasure (25/28).

Drop back down and roll through the low tunnel to reach a hallway with a pool. (This room would be dry if you came before activating the waterwheel.)

Jump into the water and swim to the other side. Climb on the ledge to the right.