...Up the lift...

Run ahead and climb up onto the rubble on the right. Break open the large salvage crate here. Then return to the lift and approach the wall on its left, where you find some arrows, and - around the corner - a box with grenades. Step towards the northern edge, facing the research base, where you will find a pillar where you can attach your rope. Shoot your rope arrow towards the climbable wall in the distance while standing next to the pillar. (Remember, you can shoot a rope arrow into the wall, if your crosshair turns red. - Which would be in the middle of the left part of the wall.) Jump onto the rope and use the rope ascender to reach the climbing wall. Climb to the right and jump past the gap towards the second part of the climbable wall. Repeat this at the second gap. Here climb up and jump towards the top ledge. Pull up. Then return to the single standing wall. Get on the other side of the wall and scramble up at the white markings to reach its top. From here you can jump towards one of the ledges at the watertower. Climb over to the left and up. Shimmy all the way around till you can pull up on top of the watertower. From here jump towards the ladder. Climb up. At the upper end jump up to reach the pipe. Here traverse around the corner to the right. Pull up onto the platform.

Enter the Research Base

You can not reach the dangling platform with a simple running jump so use your rope arrows to pull it closer. Jump over and do the same with the second platform. Jump over, pull up and - since the platform starts to fall - running jump towards the safety on the other side. Get down onto the lower level and running jump from the ramp here towards the rope, which you will then slide down. Collect the shotgun shells if you have need of them. Wall scramble up to the pipe and use it to climb around to the right. Jump across the gap to the small remains of the pipe and then again towards the right end. Follow this to the ladder. Climb up. Use the axe to traverse the wall and reach the salvage crate at the top. Jump over to the left to reach solid ground. At the top are two Solarii heatedly discussing something. I recommend wall scrambling up and hiding behind the crates instead of using the stairs. When their talk is over they should have their backs turned. Use the bow to headshot them and dispose of them silently. Loot them for salvage and pick up the rifle ammo. The large gate is closed, so approach the scrambling wall left of it and jump up to grab hold of the top ledge. Shimmy over to the left end and here jump over to the climbing wall. Use the axe to grab hold. Climb towards the left and up to the top. Here stand next to the pillar and shoot a rope arrow into the climbing wall across the chasm. Slide down. Here climb further to the left. Jump across the gap to the next climbing wall. Climb right and up to the top. Jump to the ladder and climb up. Break the salvage crate before you use a rope arrow and the rope ascender on the rubble blocking the passage. Step inside and out on the other side. At the end turn left.

Discover the Ancient Tomb

Jump towards the climbing wall and head downwards. Let go to drop down into a passage partially flooded. Wade through the water. Follow the water around the corner to the right. On the left side of the climbing wall is an XP plant. Climb up and pull into the passage. (Ahead you can spot the relic - or its empty box - you may have collected, if you had grenades.) Sneak through the narrow gap on the left. Climb down twice. In the lockers here you can find two packs of shotgun ammo. Step into the next room where the "Research Lab" camp is located. It is likely that you cannot rest here yet, as some enemies are around. On the table on the right lies the next document. Around the corner two Solarii await Lara. I was able to headshot them with the bow without them noticing. Once they are dealt with, return to the base camp to upgrade if necessary. Get back into the passage and wade through the water, to the other end. Climb up. Press the button to open the gate.

Discover the Ancient Tomb (The Elevator)

You will come towards a cargo elevator. Press its button to figure out what is going on. The elevator is jammed. Climb onto the stack of crates on the right and use your axe to remove one of the cogs. Climb up onto the elevator and out onto the upper part of the stairs the other side - otherwise unreachable yet. Head back down and pry open the door for later use. Head up to level 3. Here you find pistol ammunition and a document in the niche. You can also use fire arrows to shoot down the salvage crate above the stairs leading down. Head up to level 4, jumping across the gap in the stairs on the way. There are shotgun shells in the niche here. And overhead, facing north, is another salvage crate which can be shot down. Ready your shotgun. Call up the elevator to level 4. Before it gets all the way up, jump onto it and use the shotgun to shoot the barricade on the right. Jump through and use the axe to grab hold at the wall. Climb over to the left and jump across the gap. Use the axe to grab hold on the next part. Climb further left. At the end, drop down, collect the salvage and pry loose the cog through the opening. (This only works if the elevator is on level 4, which it should by, unless you did not follow my walkthrough all the way.) After prying the wheel loose, drop down and head further down the stairs to get back down to level 3. Climb up the ladder near the elevator controls. Through an opening on the right you can pry loose the third cog. (The elevator should still be on level 4.) Call the elevator back down to level 3. Head down the stairs. When you are between levels 3 and 2, look up to find a niche with a salvage crate. When coming from above - facing north - you can jump up there. Break the salvage crate and then pry the cog loose. (The elevator should be on level 3.) The elevator will crash down. Get back down to level 2 and jump into the elevator shaft to get to the bottom. Collect the XP crate. In the first chamber after the elevator, head over to the left. There is a locker which can be pried open for salvage. If you head into the passage, you will encounter two Solarii to the left. Rid yourself of them, before you continue exploring. On the other side of the stack is a salvage crate. Head down the passage. Head over to the right. Collect the rifle ammo. Pry open the third locker for salvage. Collect the XP crate. Head out towards the tomb. Go up the stairs to the Stormguard General.

Exit the Research Base

After the cutscene, head down the stairs. The way out will be blocked after an explosion. Head over to the right side to hide behind the stairs from the baddies appearing on the left. Get out your weapons and take care of them. An explosive barrel up on the left might be of help. Be careful, sometimes enemies come down and sneak up from the side, through the water. There will be a couple of bow-wielding Solarii, a dynamite Solarii and several rifle Solarii arrive via rope from above. The ones with rifles and dynamite are a little tougher to kill as they wear helmets. At the end you may be attacked by melee Solarii. You may simply evade their attacks and kill them with counters. (Remember: Like you learned when you first encountered wolves, or the guy with the shield, you must have used it against Boris on the Endurance at least.) Under the stairs you can find arrows on your side and shotgun shells on the other side. There are also shotgun shells by the now closed passage, by the two barrels. After the fight, search your enemies for salvage and collect any ammo left in the area. Climb up the wooden scaffold and follow the passage into the cavern. After a narrow crawlspace you will slide down a slope. Jump and use your axe to grab the climbing wall opposite. Head up and jump where necessary to reach the top. Follow the tunnel. After a moment Reyes will contact you and you will hear gunfire. Nevertheless collect the salvage crate before you follow the tunnel to the end.

Return to the Survivor Camp on the Beach

Approach the pillar and attach your rope to the roof below. Slide down. Here you will spot two Solarii with flashlights below. You may try to pull them into the abyss between you, using the rope arrow. Follow the walkway and collect the shotgun shells, if you need them and any salvage from the two enemies if you killed them otherwise. At the end you can find rifle ammo. You have to jump down from the plank in the middle of the walkway however, to a spot with shotgun shells and rifle ammo. Use the rope with the ascender to reach the metal tower from the beginning again. From this platform use the rope slide to descend to the beach. Run to Reyes.