Version: 1st draft (more details will follow in the second revision)

Mission "The Disturbance in the Sawmill": Investigate the Trinity presence in the Soviet Installation

Reach the Sawmill

Run towards the Sawmill.

Defeat the Trinity Soldiers

Fight the Trinity forces in the saw mill.

Find the Hidden Remnant

Break open the green locker on the right side of the saw to discover the hidden Remnant. (might be random?? there are other lockers around, one on the left, one on the middle level on the left) You will obtain the achievement Hide and Seek.

Mission "Chasing Grandpa": Head out of the Sawmill at the back and follow the path upwards, in the direction of the cave where you met a snow leopard. (East/North-East) Fight the soldiers on the way. Enter the cave for the "Voice of God" challenge tomb. Climb all the way to the entrance of the actual challenge tomb. If in doubt, look it up here: Voice of God Walkthrough

If you've been here before and the last part of the walkway has collapsed, you will be able to use the zip line to reach the temple. Near where you found a relic by the collapsed wooden walkway you will now find another rope attached. Slide over to the other side. Run and jump along to find a camp. Jump across the platforms and gain 100 XP. You will obtain the achievement Abandon All Hope. You'll discover the base camp Wicked Yale and get XP for it. Head up the ramp. Step outside and you will be under the influence of the witch. Turn left. Follow the path into the woods. Follow it all the way to a red room. Behind it the woods continue. Lara will relive the worst memory, before she is back in the woods. Squeeze through the gap on the left. Follow the path down and you will be dropped into a clearing. Fight off the bewitched wolves. After that you will get the achievement A Moment of Clarity.

Mission "Gathering Clues": Head up the climbable wall. Jump left to the next climbable wall and climb to the top. Follow the path and scramble up the wall. Follow the path around and up the stairs. Pry the hook on the left side of the gate loose. Run towards the rotating rope winch and tether it to the counter-weight that appeared. Stand at the lever by the chain winch. Once the counter-weight has been pulled to a position above it, activate the lever. It will crash into the door. In the chamber on the table is the next document, The Formula (6/21), which Lara collects automatically.

Mission "Making the Antidote": Use the rope arrow to tear down the barricade and to return to the base camp Wicked Vale. Sit down and you'll obtain the Camp Journal The Dreamtime. Fast travel back to the Logging Camp.

Harvest Deer Liver

There are two areas where deer can be found around here, both marked on the map. One is just north-east of the Logging Camp, the other is over on the east side. Deer may be a little shy when Trinity soldiers are around, so kill them if necessary. Then hunt down the deer. If you want to get this done quickly, use poison arrows. You have to catch and loot two to obtain the necessary livers.

Collect Seedpods from Inside Caves

Look on the map for the locations of the caves. The plants you are looking for are growing on the walls of caves. You are looking for a green ivy-like plant with red blossoms and brown seedpods.

Collect the Chemicals from the Copper Mill

Go to the copper mill (east, south-east). Kill the soldiers, one has a flamethrower. Use the ladder to climb onto the train car. From here jump to the roof of the building ahead and pull up. Then jump into the chamber on the left, where there was a rope barrier, but it's gone when you've done everything in the main game (there was a challenge there). Open the crate on the ground. You'll obtain the Amateur Chemist.

Mission "True Vision": Fight off the ambush. Fast travel back to the Wicked Vale. Get up the ramp and through the gap again. Follow the path into the woods. Here turn to the left first. Run to the fork. Continue down the right path now. After a few steps there are crates to the left and the objective is down there, too. Now run to the crates. Squeeze through the gap. Run down the path. Head further down the path and jump down onto the clearing. Tear down the rope barricade at the ruin (the other one is only for the way back). Climb up. You'll obtain the achievement Season of the Witch.

Stand next to the rope winch (A) and tether it to the one across the water (B), above the two platforms. Rotate the crank clockwise the lower the left (1) and raise the right (2) platform. Now move quickly. Get to the static pillar (C) to the right and tether this to the rope winch above (B) to hold it and the platforms (1) and (2) in position while (1) is at the lowest and (2) is at the highest.

Now run around the left side to jump towards the left, currently lower platform (1). From here jump towards the right platform (2) and on to the rope winch (D) in the south-west corner.

Stand next to the rope winch (D) and look down to the opposite side. Tether it to the rope coil in-between (E) the wooden construct.

No need to do anything else just yet. Return to the bottom. (e.g. slide down the rope)

Now cut the rope by the static pillar (C) to get the two platforms (1) and (2) moving again. But stand at the ready. You want to reattach the rope between (C) and (B) when the two platforms are almost on the same level but the left one (1) is just a little higher than (2), but not all the way back at the starting position. (It is a little tricky to get the timing just right.)

Now perform a wall scramble to get onto the wooden walkway in the middle. From its jutting ledge jump onto the rope spanning from (D) to (E). Climb up, towards D. Now use the crank here to operate the winch. Another platform (3) will be raised.

Once it's at the topmost point, release the winch. Now move quickly. Jump across the platforms (2) and (1) - which should lead upwards - and on to the upper walkway. Follow it around quickly and jump onto the other platform (3) while it's still up. Jump against the wall and scramble up to reach the top.

Video of the Final Solution

Use the rope arrow to pull the large lever the lift starts moving. +500 XP

Mission "Defeating the Witch": Get on the lift. Then pull the lever again using a rope arrow from here. You will get the achievement Last Ride of the Witch House. Jump down into the abyss to also obtain Henny Penny. Step off the lift. Follow the path to Nadia's grandfather at the base camp Witch Cave. Head down the stairs and drop into the water. Swim along. Fight off the footsoldiers. Then stand next to the rotating rope coil and tether it to the witch's bucket. Now hurry towards the lever of the boiling tank and pull it, once the witch floats above it. If you try the same at the other location, the witch will cut the rope. So act quickly and shoot her while she's being pulled along, to prevent her from cutting the rope. Again flip the lever when she floats above.

The water level rises. Swim to the south. Up the wall on the left. Fight your way through. Then get to the upper level (either up the wall on the right or via the ladder in the chamber). Here is another of those boiling tanks. You know what to do, connect the floating bucket to the rotating rope coil, shoot the witch to prevent her from cutting the rope and flip the lever when she's above the tank. Use the zip line. Fight off the enemies and then head into the passage on the right. Here you have to scale the climbable walls. At the top wall scramble up, the witch may prevent you, try again. Losen the hook on the left. Jump onto one of the floating platforms and allow yourself to be taken to the wooden walkway (second stop). Shoot the enemies. Run to the two platforms and use them and wall scramble to get up to another boiling pod. Attach the rope and then hop down to the left. Don't forget to shoot the witch to prevent her from cutting the rope. Flip the lever when she's reached her target. Use the rope arrow to get through the next barrier. Losen the next hook. Jump onto one of the floating platforms and let it take you to the north-east side. Here you climb up to the ramp from where you jump onto one of the upper floating platforms. Allow yourself to be carried to the other side. You know what to do by now. +500 XP.

Document (16/21) On the right you can find the document Grandmother Serpent. Russian (+30 XP).

Relic (1/1) On the left you can find a box with Baba Yaga's Broom.

Document (17/21) Turn to face the back wall and use wall scramble to get up there. In the niche you will find the document Control. Russian (+15 XP).

Survival Cache (4/6) Jump off at the wooden walkway in the south and run towards the two platforms that would lead to the upper walkway. Instead of taking them, drop down. Find the Survival Cache at the back wall in the middle. Then use the wooden board and the handholds to get back up again.

Document (19/21) OLD VERSION (Beware: It seems I described a method that was not planned, this path is no longer available on the PlayStation 4 and has possibly been patched in most or all versions, see box below for the regular solution.)
Stand next to the rope coil. Turn to face the direction you came from (east). Above you can see another rope coil. Attach your rope there and a platform on the other side will be raised for a short moment. This is a tough time run, so don't waste any time. (You do remember how to sprint, don't you? Xbox: press the left stick.) Run towards the two dangling platforms at the wall and jump across them. From the next ledge, jump across the remaining two of three platforms. (Make sure you jump off at the latest moment, to make it without wasting too much time, if you have to pull up more than twice, you'll not make the run. Better make it only once.) Once you reached the other side, run over to the right wall and from there climb up onto the ramp. Here you quickly run upwards. Jump towards the hopefully still raised platform. From here jump over to the other side and when necessary use the grapple (acquired late throughout the base game) to reach the next document, Not Worth Living (Russian +15) lying in the alcove. Get back down, by dropping off the ledge.

Document (19/21) Stand next to the rope coil. Turn to face the direction you came from (east). Above you can see another rope coil. If you attach your rope there, a platform on the other side will be raised for a short moment. Now you have to be careful with your timing. Look towards the rotating platforms in the middle of the chamber. Note the one on your level. Wait for it to come past the high wooden ramp in front of you. Once it's there, use a rope arrow to connect the two rope coils. Don't hesitate but make your way onto the platform which should now be close to you. Now be patient and ride around the circle till you reach the wooden ramp. Jump off and run ahead to jump to the raised platform. It may be necessary to pull up. Hurry and jump on towards the safe platform with the document. If necessary get a firmer grip or even use the grapple from later in the game if you have it and pull up. Collect the document Not Worth Living (Russian +15) lying in the alcove. Get back down, by dropping off the ledge. (Video: youtube)

Document (18/21) Your destination is the brightly yellow painted passage lit by a torch. You have to get out after the pile of rubble, at the section where there is no wooden ramp to easen your jump. On the right, by a pile of rubble, you will find the next document, Dreams from the set "Dreams in the Witch House". It will improve your Russian (+15 XP).

Survival Cache (5/6) In the north-west corner you can climb up into an alcove. Here you will find the next Survival Cache.

Map: Then continue on to the right and into the tunnel. Here you climb down into the chamber to find the Archivist Map Use a rope arrow to tear down the barrier.

Survival Cache (6/6)Head through the arch right in front. In the left corner you can find the Survival Cache.

Explorer's Satchel: In the right corner you can find an Explorer's Satchel with another map. +50 XP.

Document (20/21) Once you're at the top, look to the right. Use the grappling spot to swing over to the other side and obtain the next document, The Last Word. Greek +30.

Document (21/21) Now get into the water tunnel and swim along till you can turn left. In the Chamber you will find the document The Coming Madness. Greek +15 XP. Return to the chamber with Nadia.