On this page of our guide to Uncharted 2: Among Thieves you will find a detailed description of secrets and collectibles available in Chapter 17 - Mountaineering. Our step-by-step walkthrough explains how to find all (6) secrets hidden in the 17th chapter of the main campaign.
The first secret is almost at the very beginning of this chapter. After using the first rope, you will have to go down the ladder to the bottom of the cave. While being at the bottom (before you go through the tunnel in the footsteps of a Tibetan), look around and walk through the available area to reach the cliff. There's a treasure hidden near the edge.
The second treasure was hidden on a small stone ledge in the place where you will reach the camp (where a cutscene with wolves is being displayed) to bring the second rope to Tenzin. Once the rope is attached to the vault, use it to get to that shelf and not follow your companion right away.
The third treasure is hidden near the area where thin ropes will be attached to one of the walls (after crossing several ledges covered with ice). Only one rope can be grabbed. The valuable item is located on a rocky ledge - to the left of the aforementioned area (you have to jump down).
The third secret is near a spot where water is going to soak your shoes. Once you have reached the water stream (before that, a part of the vault will collapse behind you, cutting your way back), follow the water current. Before the waterfall, as you look towards the chasm, turn right and walk on the narrow ledge to the very end. That's where the treasure is hidden.
The fifth secret is not far from the previous one. After climbing the rocky ledges near the stream, you will reach a place where you have to jump over the water below in order to get onto the opposite ledge (a ladder will be visible in the background). The treasure is located on the aforementioned ledge, on the left side. This is a necessary path that is required to complete the chapter, so you shouldn't have any problems finding this place.
The last hidden item is located on a narrow ledge (just before the end of the chapter) near the place where you have to knock off a rope by shooting at a crate (the treasure is a bit earlier). Examine that place carefully, and you'll notice that ledge leads into the rocks. Walk between them and collect the treasure.