Hidden items are located in the following locations:
-On a shelf in the back left. -Below the stack of books at the left edge of the screen. -The golden toucan statue is sitting on one. -Behind the stem of the large goblet in the middle of the bottom edge of the screen.
Check above the golden mask to the left of the sarcophagus. It is a bit behind the mask, and the top edge of the cube is horizontal.