I (mostly) figured out the numbering system, and figured out the bell level; it doesn't have any icons beside it anymore, but it's still not turning gold. Why not?
Why isn’t the bell level turning gold
fez
Related Solutions
The square symbols on the bell's four sides are numbers (1, 3, 6, and 10) that represent the amount of times to ring each side. Any order should work. The bell disappears forever, replaced by an anticube.
The 16-cube area is the ancient version of the temple/science warp zone. That QR code was under construction long ago, but it now appears "fully realized" on the same wall in the temple/science warp zone. So it can be completed—indeed, it has been.
If you're curious, the QR code links to...
text: "RT RT LT RT LT LT LT RT" (which triggers an anticube, as shown above)
This is a higher resolution of the screenshot, from the PC gersion of the game:
I have then extracted the QR code, converted it to black and white, removed Gomez and some dust, and applied a median filter. This is the complete QR code, which you can scan on a website.
Best Answer
In Fez, a room does not turn gold until you do all of the tasks corresponding to the icons, as you have discovered, and you find every exit from the room. This means that in your situation, there is a door that exits from the bell level that you have not yet found.
Most likely, you have not yet lowered the water. There is a puzzle in another nearby level that will lower the water level in several levels including the bell level. When you do that, there will be another door that was previously below the water line but is now accessible.