Entrance coordinates: [712485; 3415986]
Note: You can explore this tomb only on your way back from the Endurance wreckage, which is after acquiring the rope ascender from the mini boss you fought on the main deck. Start exploring the beach near the survivors' camp (northern area of Shipwreck Beach) and you'll find a barricaded entrance to an underground temple. Shot a rope arrow and use the rope ascender (hold the action button) to unlock further way.
Go down the linear corridors, using the torch to light the way. When you reach a cavern with a waterfall, don't create any rope bridges - you can just as easily wade through the stream. Soon you'll reach the main chamber, a new base camp and another puzzle to solve.
First, approach the mechanism near the base camp. Use the climbing axe to raise the cage and let the buoy swim to the left.
Let go of the mechanism and quickly go left, scrambling up a ledge.
Keep running until you reach a new edge. Wait for the buoy to hit and turn the first interactive mechanism. As soon as you see the beam in front of you, use it to leap over to the next ledge.
Continue running ahead until you reach another edge. Look down and shoot a rope arrow at the indicated spot in order to turn the second mechanism. You need to do it before the buoy reaches it.
The next step is practically the same; wait until the mechanism turns when the buoy hits it, then leap over to the beam.
Leap again right away, and make sure to use the climbing axe. Pull up to conclude the puzzle.
Enter the last chamber. Locate and open the chest to find 250 Salvage points and a map of GPS Caches (reward: 1250 XP). Backtrack to the exit.