On this page of our treasure guide to Uncharted 3 Drake's Deception you can find valuable information about all collectibles available in chapter 7. There is only one treasure in this chapter. You can get this secret as soon as you escape from a spider-like creatures.
Gold and Pearl Stickpin
After escaping from the spiders jump through the hole and start looking for a way to the other side of the room. When the ceiling collapses, Sully will join you. Climb up on the collapsed ceiling and turn towards the direction from which your companion has arrived . Jump to the ledge from which the ceiling collapsed and take a few steps straight ahead to find a treasure .