The first world/area shows an "incomplete" room (white node) with many paintings, most prominently one of a monocled guy. What is the secret to this room?
Look at the painting with many fezzes. The hats are a code:
RT RT LT RT LT LT LT RT
This anti-cube will auto-complete a QR code room later in the game. Vice versa, if you complete that QR code room, the monocle room will auto-complete (white node on map → gold).