The Silver Inca Vessel is the fifteenth treasure that can be found in Uncharted: Drake's Fortune.
The Silver Inca Vessel is found in Chapter 4 - Plane-wrecked. This cool-looking treasure is in the little section right before you discover a section of Sullivan's crashed plane. In this area, you have to jump from a slanted narrow slab of rock to a slanted log. The treasure is fairly easy to spot: it is to the right and below the log, in the corner of the rock wall.