WHAT İS THE CODE MAN!!!???
Spoilers (Scoring through text to make it a little harder for people to see hints if just scrolling through comments cos I don't think there's a proper spoiler formatting here):
The note on top of the safe gives you the hint for the code. If you've found the key that opens the box you now know what direction north is. Every wall has something on it that can be counted to get the code.