How do I solve the Puzzle?
When you hit Escape during the game, one of the options that can be selected is "Puzzle". It looks like a series of boxes, and presumably since it's named "Puzzle" it can be solved in some manner. How do I do that?
There are little glowing collectables in the game (picked up with right mouse click). (I found them while using the Rasmus mask [2nd from top]; I don't know if you have to have it on to see them.) There is one in Chapter 6, second floor, on the balcony just after you climb out the window. It is under the second tree, but should be clearly visible. It will be a letter.
Each of these letters will slot into the puzzle accessed by pressing Escape in game.