After the cutscene showing a chopper chasing Lara's and her guide's jeep, the heroin will fall down and land on a rock ledge. From there, the city can be seen. Go forward through the narrow passage until you reach the rocky wall.
Jump on the wall, Lara will hang on the ledge. Move to the right. Once the girl reaches an overhang in the corner of the rock giant, jump up and pull yourself up.
You will see a passage leading to one of the temple's tunnels. Get close to it and Lara will walk to the other side.