Chapter 10: Berlin Catacombs
When you cut through the first gate you come to, drive forward a wee bit and look to the left to see a pipe in the side of the rock that is blowing out bubbles. Just to the right of the pipe will be a small opening that you can swim through. Follow the passage and it will eventually lead you to a small room where you can find letter on the left of the room beside a mattress.
In the same room as the letter, you will see this as soon as you walk in on the left side, sitting on a spool.
When you need to reposition the Pump Wheels, do so and then drive through the two turbines and this treasure will be on a platform to the right side just after the second wheel.
From the platform where the gold ladle was, go through the tunnel to the left of it and follow it through to the previous room you were in with the pillars. Go to the far side and on the right will be a small tunnel going downwards. At the bottom will be the snake.
Now that the area has the water level raised, go back to the large room before the Pump Wheels and go to the other side of the rubble. On the right side will be this open door that you can now reach. Go inside and the lantern will be on the ground.
To find this, you will need to release the two mines in the first area where you begin needing to swim. Go through the tunnel, all the way to the end and then go up the stairs on the left and go through the door that has a chain on it. Drop through the grate to the ledge below and crawl through the tunnel there. Climb the ladder and go through the open door at the far end to find this there.