easter egg things: I found a a white ? cube in the spot of the 1973 cube that spawns when you start the game but goes away when you get close. A weird song plays when you stay ontop of the largest cube cube in the main area. There's a weird picture underneath the area with the rotated rainbow cubes. And I found a moon near the art gallery in the second area.
That’s a pretty good run down of the easter eggs in the game. The China Cube and the Other Massive Easter Egg Nobody Will Ever Find are both random chance things, so don’t worry too much about finding them unless you love restarting the game over and over.