Temple of Karnak (Location)
The giant temple that dominates the northside of Thebes. You'll pass through here several times during the main quest.
The eastmost treasure is on a lower level, you'll need to take the stairs down to find it.
The treasure itself (a box of carbon crystals) is on a small desk there.
The next treasure is also in the east wing, back on the upper level; in a red chest in the sleeping area.
The last treasure is all the way at the west end of the complex, at roof level. Look for it above the doorway past the ornate columns.
Climb up and loot the red chest there to compete the location.