Walk left and jump on one of the pillars of the aqueduct. Notice that all places where you can perform a jump are marked with a white paint. Perform a double jump and Lara will catch the ledge.
Move left and jump to the other side of the hole in the wall. Then, walk up.
Walk further left through the wooden beam. At some point it will break and Lara will fall below.
Perform few more jumps towards the entrance to the main part of the temple. Jump to another ledge, move right, jump right above the niche shown on the picture above and climb on the solid ground. Jump into the hole that is the entrance to the temple.
Lara will start walking through a dark, narrow corridor. At its end use your leg to break the stones that plugs the tunnel. When the Y button sign will appear on the screen, press it on the pad. Repeat this action twice.