Indiana Jones and the Great Circle truly has mysteries around every corner, including the literal "mystery" side quests found throughout each level.

Inside the Apostolic Palace, which sits directly above the dig site in the southeast corner of The Vatican, there is a strange bookcase that contains one of these hidden mysteries.

Find the Bookcase Note's Hidden Code

In the green-colored office at the top of the Apostolic Palace, there is a note sitting on the desk by the door. The note explains that there are four latin books on the bookshelf that must be "taken alphabetically."

If you flip over the note , there are four symbols with corresponding words written on them. These symbols are also found on four of the books on the bookshelf in the room.

Pull the Books in Order

Grab Mussolini's Letter

Once you have pulled them in the correct order, a secret compartment will open up and reveal a nice wad of cash, as well as the Mussolini's Letter journal note, which will complete the mystery in your journal when you collect it.

The best hidden references and cameos we were able to find in our globe-spanning adventure!