SOVIET INSTALLATION - THE RED MINE CHALLENGE TOMB
CHALLENGE TOMB ENTRANCE: In the part of the old mill where you first learn to craft molotov cocktails, there is a side room with a strongbox. (This is described in the main walkthrough.) At the far end of this room is a console with a green light. Use it to open the large metal door with the painted glyphs. Enter and follow the tunnel to a fork. On the left is an Archivist Map (7/9), which reveals the locations of various collectibles you've already found if you followed this walkthrough. There's some magnesite ore in a dead-end passage to the right. (screenshots)
Follow the main tunnel to a ledge overlooking a vertical shaft. You can ride the zip line down, or climb down the ledges on the right to find more magnesite, then wade through the shallow pool to reach the ledge where the zip line ends. Continue to a flooded area. Swim forward to another fork. There's a flashing light in the dead-end passageway to the left. This is a survival cache (16/21). You can dig it up now even though it's not shown on your map yet. Swim back to the main passage, make a U-turn to the left, and keep going. (screenshots)
When you emerge from the water, take cloth and a bottle from the boxes, craft a molotov, and use it to burn the flammable barrier so you can continue. Jump across the open shaft to grab the ledge on the other side. It does not hold, and Lara tumbles down a chute into a lower tunnel. (screenshots)
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). Then 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. Once the flames die down, jump through the water, taking care not to fall down the hole below, and enter the tomb. (screenshots)
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, they will also be marked.) Continue down the tunnel to the Excavation Shaft Base Camp. (screenshots)
THE RED MINE CHALLENGE TOMB: Jump from the ledge near the Excavation Shaft Base Camp to the platform with the single mine cart in the middle of the huge pit. The ledge collapses, and you must quickly press Interact to avoid falling. Then climb onto the platform above. There's a flammable barrier off to the left, but a torrent of water from a broken pipe above prevents you from throwing a flaming bottle into it. Jump across to the wide ledge on the far side of the room. There are boxes of cloth and bottles here, but since you can't use them yet, just head up the stairs. (screenshots)
Scope out the puzzle. There's a track with 2 mine carts that ends near the torrent of water. The first cart is being held back by a dangling bucket of uranium ore, which is attached to a second bucket suspended near the ledge where you're standing. There are also more mine carts lined up at the top end of the track in case you need them later. Start by jumping from the red ledge to grab the closer bucket. Lara's weight lowers the bucket, raising the second bucket and freeing the mine cart on the track above. The cart then rolls down to the end of the track, blocking the flow of water in front of the flammable barrier. But it's not that easy. The second cart then rolls down the track and crashes into the first. Then the track collapses. With nothing holding it back, the water continues to flow. Back to square one. (screenshots)
While you ponder the mine cart puzzle, make a few pickups. When Lara drops from the bucket, she lands on the lower ledge. Return up the stairs. At the top, turn around to spot a relic (15/18) sitting on the crate. It's a Bomb Fuse for an improvised explosive from the Gulag Possessions set. In the little room to the right of the room with the codex, there's another Greek document (22/26), Discovery from The Red Mine series, and locker with some salvage and arrows inside. (screenshots)
Run up the wooden ramp to reach the ledge above and to the left of the staircase. Turn around and use the horizontal pole to swing across to the ledge above the room where you found the document. Examine the mural (10/12) on the right wall to gain XP and increase Lara's Russian proficiency. (I think this one is All Empires Fall from the Soviet Crests series.) (screenshots)
Now climb up on the left (opposite the mural) so you're on the roof of the room with the codex, overlooking the buckets and mine cart track. Shoot a rope arrow into the mine cart at the top of the track to pull it out from behind the barrier. The cart then rolls down the track until it is stopped by the dangling bucket. Move around to the right. Stand near the rope-wrapped post and turn away from the open room. There's a small crawlspace at the back of the room. If you follow it to the right, you'll find a container with some cloth and a gold coin.
Return to the main room, stand next to the rope-wrapped post, and shoot a rope arrow into the mine cart you just freed. Lara automatically anchors the rope, tethering the cart to the pole. (screenshots)
Climb back down and move around to the red ledge. Jump to grab the bucket once more, pulling it down and raising the other bucket so the cart can roll off the end of the track. Since the cart is now attached to the pole above, it swings forward blocking the flow of water. Victory! (screenshots)
Pick up a bottle and craft a molotov. Then throw it at the flammable barrier. Once the flames subside, jump over to the opening you just made and climb inside. In the upstairs room you'll find containers with cloth and a Byzantine coin, 2 more coins lying in a pile, and the codex. Reading it unlocks the Bright Eyes skill, which automatically highlights nearby traps in red. You also receive 10,000 Expedition Credits the first time you raid this tomb. Exit through the tunnel to the right of the codex, where you'll find a box of supplies, 2 more coins, and another survival cache (18/21), buried on the left. (screenshots)
EXITING THE MINE: When you have everything here, scramble up the wooden wall and climb onto the ledge above. Now ascend a ladder, two climbable walls, and another ladder. Pull down a rope-wrapped wooden barrier and move forward into the tunnel. Ignore the passage to the left, which leads back down to the tomb. Continue forward. When you come to the falling water, jump over the deep shaft, and keep going. Swim through one flooded section, then another, and finally climb several ledges and one more ladder to get back to the tunnel that leads to the COPPER MILL.