This page of the guide has a walkthrough for the second part of chapter 18 of Uncharted 2: Among Thieves called Heart of Ice. The main character must again interact with gears and other mechanisms. You have to jump on narrow platforms and defeat some mountain monsters.
You reach a place where there are several gears next to each other [secret 3]. Climb towards the one that can transport you up. Catch it from the side, let it transport you up and then grab the ledge on the left.
Jump on the wheel again, this time from the top, and get to the other side. Walk on the brick platform and jump over the hole to reach the lever. Pull it up and watch the cut-scene.
Use the nearby ladder and go down to the snow-covered shelf at the bottom. Reach its end and jump towards the chain. Hold it and run on the wall - swing and jump towards the beam in the darkened part of the map. Jump down twice to reach the only structure that wasn't damaged.
Go left and catch the golden decorative elements, the ones near the gear. Grab the gear and make your way to the other side. Jump towards the pole.
Swing and then jump towards the mechanism with chains and weights. They move up and down alternately. Grab them and remember to change the position accordingly. You have to move towards the top of the stone shelf. Don't move between the weights by jumping - simply tilt the analog stick in the right direction.
When this sequence is over, look around to find another rope. Jump towards it and then jump to the wall near the next gear. Find protruding bricks. Grab them and go down. Then grab the gear and go down to the platform below.
Go around the wheel used earlier. Then use it again. This time, however, you will move upwards [secret 4]. You will come across another wheel - grab it.
You will reach the third gear. Climb it and jump towards the pole. Swing on it and jump to the snow-covered ledge [secret 5]. Go left and climb the stairs leading down into the ancient "stairwell".
You will come across a pressure plate. Stand on it to make platforms slide out. After a short cut-scene, go down the stairs to reach said platforms.
Jump to the first one and then on the pole. Next, reach the next platform and then jump towards another pole. Reach the last platform and go to Tenzin. The only difficulty may be that these platforms will retract after a few seconds. You have to be fast.
Watch the cut-scene and cross the bridge. Move towards the big statue [secret 6]. When you reach the giant statue, you will find the entrance to the room.
Inside, go up the stairs to the place located opposite of the entrance. You will come across a lever. Pull it and get ready for a fight.
You get attacked by the mountain monsters. You don't need to defeat them, simply survive long enough until the elevator arrives. Be on the move at all times to avoid the monsters. The creatures have a new attack - they can throw boulders. Avoid them by running around the arena.
When the elevator reaches the bottom, jump on it and wait for Tenzin. One of the monsters will join you. The creatures grabs Nate - you have to shoot it in the head several times. Throw the enemy off of the elevator and watch the cut-scene.