The Antique Ghau is the sixty-eighth treasure that can be found in Uncharted 2: Among Thieves.
The Antique Ghau is found in Chapter 19 - Siege. As soon as you emerge outside, you'll be able to grab this treasure. From where you climbed up the ladder onto the roof, face leftward, and then jump down off of the roof to your left. There should be a building lining this part of the screen, with a tree growing nearby. Along the base of the tree is this treasure, so be sure to keep an eye out for its telltale glimmer!