Geothermal Caverns - "The Pit" - Part 2

Turn left and go into the other northwest tunnel opening, the more brightly lit one with the broken bars. There are men—or what used to be men—in the cages here. Killing them nets a small amount of XP. If you want to do it, use use rope arrows to conserve precious ammo.

A little way in there's a GPS cache (2/5) lying on the ground on the left. Just beyond this cache is a wooden ledge.

Climb up to find a small cave with a salvage trunk. Pry it open, drop back down into the passage and turn left.

Shoot a fire arrow at the sack (3/6) hanging from the ceiling—one more for the Firestarter Challenge.

Continue to the end of this tunnel to emerge back in the main cave. Climb the stone steps on the northeast side.

Use your axe to crank open the gas valve. Quickly move out of the way to avoid breathing the noxious cloud.

Stand at a safe distance a shoot a fire arrow into the gas billowing out of the pipe

The resulting blast destroys the door so you can leave this area.