One code is found by going to the northwest corner of the map, to a big room full of water and blue furniture. The one you are probably missing is found by heading east as far as you can. There's a water passage going east that leads to a gap, with a teal colored room on the other side. You have to freeze the water (press Z while near it), and then slide across the Ice to jump over to the teal room. Then just proceed until you find the code on the wall.