Copper Mill - Red Mine Challenge Tomb (Part 2)

After falling down the mine shaft and sliding into the lower tunnel, as shown in part 1, head downhill to the right. (It's possible to climb up on the left, but this just leads back to where you started.)

When you reach a landing with several straw-packed wooden crates, go to the right for some salvage and another survival cache (17/21).

Continue along the main tunnel. Just before the next small room, the floor gives way...

...and you must press Interact to make a saving grab so Lara doesn't fall to her death. (You could also jump over the weak floor.)

Pull up and enter the room, where there is a flammable barrier behind a leaking pipe. First examine the relic (14/18) sitting on the desk, a Hip Flask from the Red Army Officer set.

Then grab a bottle and cloth, craft a molotov, and throw it over the pipe so the rushing water doesn't extinguish the flame before it reaches its target.

Wait for the flames to die down.

Then jump through the water, taking care not to fall down the hole below, and enter the tomb.

Jump down to the brightly lit ledge on the left. Enter the tunnel and immediately turn left...

...into a little cul-de-sac with a document (21/26) written in Greek. This is Resistance from The Red Mine series.

At the bottom of the steps just below the document, hidden behind a rusted mine cart, is an Explorer Satchel (5/6). Examining it reveals the location of a survival cache on your map. (If you didn't find the last two caches, above, they will also be marked.)

Continue down the tunnel...

...to the Excavation Shaft Base Camp.