This is a labyrinth cube. A labyrinth is a maze without wrong turns. This labyrinth is 2.15 x 2.15 x 2.15 inch (≈5.5x5.5x5.5cm). There is also a small foot on one edge so that printing can be done cleanly without any support. The holes are 0.26 inch, thus any ball 0.25inch and smaller should work. 

This is a challenge test for your printer. If you get stringing, this labyrinth will not print without blocking holes.

Modeled with and without windows. Even with windows you can only confirm what floor of the labyrinth you are on.

Ball STL included.