Theres one sitting in a cage hanging above the hole in the floor that drops down to the room with all the runes
One that appears in the main area of the academy if you run up the ramp that appears with the helmet on
One that appears after using the 4 pressure plates, one of which being only visible with the helmet on
One that appears on an alter after matching colored torches in the hallway, the matching torches only appearing with the helmet on
One that sits at the top of the room with all the beds, which is accessible after pulling the lever in the secret room enterable when wearing the helmet.
