Geothermal Caverns - Guarded Tunnel with Base Camp - Part 1

Follow the tunnel up two sets of stone steps. Just ahead, where the tunnel widens, 3 of Mathias's men approach from the opposite direction. As soon as Lara hears the oncoming enemies, she'll go into a defensive crouch. Grab the 3 bundles of arrows leaning against the wooden fence in the middle of the tunnel. Then hurry around to the right to hide from the men.

They'll have a little conversation. Then one will return to the area farther up the tunnel, and one will head down to the pit to check on the valve you just destroyed. The third will stand on the other side of the rock formation for a nice, relaxing pee.

While he's relieving himself, you can kill him with a silent headshot...

...or sneak around behind him and use a melee attack. He makes quite a bit of noise if you hit him with the axe, but the other men don't seem to notice. Sometimes you've just gotta go that badly.

The guy who went into the pit will call out, "Hey! We got a problem. Get down here!" But he doesn't seem to notice that the man you just killed doesn't respond. If you return to the pit to look for him, he seems to have vanished. Maybe the prisoners got him.

Search the guy you killed. Then collect a GPS cache (3/5), food cache and edible plant against the right tunnel wall, near where you hid.

Sneak up the steps where the third man went.

He's sitting in the well-lit area ahead playing checkers with another soldier. Grab the arrows leaning against the wooden wall and watch the men. After a moment, without your doing anything, the spotlight burns out. The man on the right goes to investigate, while the demo man remains seated.

Take him out with a silent headshot.

Then do the same to the other man while he hunches over the spotlight. If you don't take kill him quickly, you may still be able to hit him before he starts yelling, but if either of them notices Lara, he'll call out for help. Then you'll need to fight a bunch of men at once. Likewise, do not ignite the gas near the guys playing checkers. This will also bring in more enemies.

Afterward, loot the bodies and pick up a document (2/3) sitting on the floor near the checkerboard. This one is a letter from Reyes to her daughter, part of the Endurance Officers series.