Once you are in the ruin, go up the stairs and jump and grab the wooden plank at the top. Use your vision to spot the areas you can use to climb around the wall to a safe landing spot. Go to the point where Lara says “It sounds like there is alot of water down below” or something to that effect. Once inside you will need to work your way to the Cistern Cavern.
In order to gain access to this Tomb you will need to shot the Log above the wooden floor at this location on the map.
