Someone has built an enormous temple in the middle of the Tibetan mountains, and it's your job to get to the center of it to find out the fate of Schäfer's expidition. It's just you and Tenzin, but you'll take different routes, so it's more of a solo effort in actuality. The untended machinery still runs and you'll have to use that to your advantage to get where you're going and clear obstacles for yourself.
Cross the cylinders[edit]
Go down the path and the steps to find yourself in a huge, underground temple in the middle of a mountain. Head to your left as you enter and stand on the square switch in the ground there. When Tenzin stands on the opposite one, the pillars behind you will go down and you can get beyond them to another switch that will lower the pillars on Tenzin's side. From there, head up the short broken steps and jump to the cliff. Climb up to a golden rod sticking out of the cliff face, and when you hang from it, it will activate a mechanism that pushes some ledges out for you to scale. You have a limited time here, so jump over to the pushed out blocks and hurry up them, going from side to side when needed. When you get to the top, grab the ledge and go right after the blocks retract. This will take you around to some pegs you can swing across to a pillar with handgrips on it back down to the ground.
When you get down, go up the steps and follow the path around, but go down to the right instead of up the second set of steps. These steps lead down to a little hideaway with a switch you can pull. The switch lowers and rotates the cylinders over on Tenzin's side of the cavern, and his switch does the same for yours. Head back up the steps and follow along the path the other way this time. Jump over to the first spinning cylinder and climb up a few rungs so you'll be able to jump to the next one when it spins around. The only thing you really have to watch for on these are the narrow walls going down the sides of the cylinders. When you're on the second cylinder, drop down a bit to get under the both of the walls then jump to the third one on the other side. There will be another wall on this one you should go under, then ride it all the way around so you're facing Tenzin's side of the cavern. On the rail right under the wall on that side, you'll find the 060Mandala Thogchag. Head around the cylinder back the way you came and jump to the ledge on the side that you passed before.
Through the machinery[edit]
Go through the archway and jump to the wooden beam sticking out from the wall on the left, and from the end of it, jump again to the snowy handholds on a piece of wall in front of you. Climb up and to the left, then jump to another wooden beam on the left. Take this beam over to a platform where you can jump up and grab onto the side of a large spinning cog, which will bear you around to the right and another platform. Close to where you drop down is a short chunk of beam pointed out toward a vertical cog with its teeth spinning upward, from your point of view. Go the end and jump out toward the cog where you'll catch a wooden post and be able to swing jump the rest of the way. Take the cog to the top, and you'll see a large spinning wheel on the right with some spokes missing. You'll need to time it well to jump through that gap when it comes around.
On the other side, jump up onto the side of another large gear and take it around to the far wall. The climbing detection at the wall is a little touchy, so rotate the camera around to the right, closer to the wall (meaning the camera itself, not what it is looking at) to make the transition easier. Climb to the right then jump to a beam and drop down two more beams. From here, face back to the inside of the temple (away from Tenzin) and look directly to the right to see a post sticking out of the wall. Jump to it, then swing jump down to the top of the cog below. Down there you'll be able to jump to the rope hanging out in the middle of the open space. You'll want to jump to the snowy ledge right above the vertical cog across from the one you just left, but before that, angle to the wall fragment to the right of this and pick up the 061Dipa Oil Lamp while you're swinging. When you do jump to the snowy ledge, it crumbles under you and you'll ride the cog down to a lower level.
Off the side of this new area are two horizontal cogs forming steps down to a larger vertical one. As you're looking down these "steps", go to the right side of the top cog and hang off the side. This will take you around to the 062Tibetan Flint Lighter on the understructure. When you've got it, go down to the bottom cog and jump up onto the teeth of the vertical one on the left so you can ride it up. Climb left at the first ledge, then shimmy around so you can get up on top of it. Now you can ride the side of the big cog you just left up to the very top where you can jump across to ledge and pull a switch outside. The cylinders all fall down during a cut scene, but when you regain control, you'll be right above a white ladder you can take down below. At the bottom, follow the snowy ledge and jump to the chain against the wall and do a running wall jump to a beam where you can drop down a couple times to one that spans the narrow part of the gorge.
To the bottom of the temple[edit]
On the other side of the bottom beam, jump up onto the gold squares and cross the side of the vertical cog. Go around the corner and drop down to another beam, then jump to a golden bar off the side. Line yourself up, then swing jump to the square pulleys going up to the ceiling. Circle around the side to the left, then jump across the other square pulleys going in alternating directions until you get to the last one going down, from which you can jump to the ledge on the far left. Make sure you take the pulleys up high enough that you'll be able to make the jump as you're going down from the last one. Once you're on the ledge, you should see a short beam going out toward a rope hanging down out in mid-air. Jump to the rope and swing jump to the far wall. Climb down the wall as far as you can go, then move left to get onto the side of the vertical cog there, and ride it down to the bottom. Jump to the ledge in the direction of the distant snowy peaks, and go around to the platform right below that same vertical cog.
Jump up onto the teeth of the cog and ride it all the way to the very top where you can jump up onto a beam on the right. Walk back toward the camera, going down over the side to skirt the post in the middle. When you get to the end where it breaks off, move the camera so you can see back away from the cog across a couple more beams to a ledge on the other side of the ceiling where the telltale treasure light is shining. Jump the beams and then to the ledge to retrieve the 063Bronze Dorje. Go back the way you came, but go one extra beam farther than the one you started on and walk off the end of it to the horizontal cog below. On the other side of it, you can jump to a white peg in the wall then swing jump to a little snowy ledge. Go to your right into a little alcove where a statue has been carved into the wall. Shoot out its glowing eye and you'll be rewarded with the 064Tibetan Ceremonial Axe. Go back to the little ledge and around to a place where you can get up and go down some stairs.
Discover the party[edit]
Head down some steps and stand on the switch at the landing. This raises some platforms, and Tenzin will jump over to a central one and depress the switch there. When you leave your switch, you'll have a limited amount of time to run down the steps, and start jumping from platform to platform to join him. Go down the stairs and jump off the side to the first platform directly in front of you. Turn to the left and jump to the peg sticking out of another platform. This is another switch, but you can still swing jump to the platform ahead. Turn to the left again, and jump to the next peg where you can swing jump to a higher platform. From there you should be able to make it to the one Tenzin is on to stand on the other switch. This causes the main statue to turn around and a platform bridge to it to rise up out of the water. In between the eyes of this side of the statue is a treasure, and if you're very quick, you can aim up on the second to last platform and shoot it down before the bridge descends back into the water. It can help if you move the camera up while running on the third to last platform. This helps your aim to be close to the crown before shooting. You may want to wait until a second run through when you can buy the Dragon Sniper and spawn it on this level, for an easier time of it. The 065Trigram Thogchag falls down at the top of the steps leading down, so pick it up before heading into the next area.
After finding Schäfer's expidition, you'll hear the growls of the snow beasts, so it's time to get out of there. Take the stairs up behind the statue at the bottom that's gripping the big blue stone. At the top you'll find a switch you can pull with 
. This lowers an elevator from above, but not before you're attacked by two of the beasts. Don't bother overmuch with trying to take them out, just maintain your distance and take pot shots at them if you want. It's best to stay right by the switch, because it's from there you'll need to jump to the platform when it's lowered. The beasts throw large boulders, so be on the lookout and dive out of the way when they do. Eventually the lift comes down and you can jump to it from the side right where you pulled the switch. Drake will yell for Tenzin to get to it, which will alert you it's time to go if you're not up there already. Jump to the elevator and shoot the beast's face full of bullets when it jumps on after you think you've made your getaway. After that it's a nice peaceful ride out of the mountain temple.