Geothermal Valley - Pit of Judgment Challenge Tomb (Part 4)

Swim back across the pool...

...and enter the codex room.

Here you'll find 2 clumps of mushrooms, a container of cloth, a box of supplies, and the second document (18/33) in The Pit of Judgment series, titled The Overseer (Greek). Of course there's also the codex itself, which unlocks the Geologist skill (plus XP and 10,000 Expedition Credits).

This skill allows you to find chromite ore, which can be used for certain advanced weapon upgrades and outfits that involve armor plating. Now whenever you mine magnesite, there's a chance you'll also get some chromite. There's a vein of ore on one side of the treasure room where you can try this now, plus 2 lumps of ore in the doorway leading outside. Chromite is listed under Exotic Resources in the Resources section of your Map/Inventory screen.

Swim back across the pool toward the entrance.

To bypass the slippery slope where you came in, climb the rough wall on the left to the ledge above.

Latch onto the next section of climbable wall and climb up and to the right. Jump across to the right and continue climbing onto the ledge above.

Go through the low tunnel with the dangling roots.

Return across the fallen tree.

Then jump across the chasm to the climbing wall on the right. Climb to the left and upward until you reach a pair of thin, stone handholds.

Continue climbing around to the left until you can drop down into the tunnel that leads back to the Hidden Ravine Base Camp.