Ceremonial Mask

The Ceremonial Mask is a treasure found in Resident Evil 5. It is one of the very many treasures needed for the They Belong in a Museum Achievement/Trophy.

Location
In Chapter 3-1, at the end of the level, there is a tunnel near the ending of the chapter, just before the trolley.

You will find a treasure chest inside the tunnel, which ofcourse contains the Ceremonial Mask.