Attached is another midnight doodle.

Necker Cubes can cause your visual system to flip back and forth between two possible interpretations; depending on where you look the cubes seem to pop inward or outward. I wondered how adding a realistic "door" into each cube would affect this perception. Making it realistic required some extra attention to detail. I gave the animation a spin-hold-spin rhythm.

If would be fun to Escher-ize the whole thing by adding windows and staircases and potted plants.

Enjoy!

John