Recommended age: +9 years. Number of players 1. Box size: 12,5x11x11cm. The hollow cube is the latest technical innovation in the world of brain teasers. This cube is surprisingly unique in that it has no centres, allowing you to see how the segments move. It's beautifully designed, but that doesn't make it any less challenging than a normal cube. Rotate and flip the cube to mix the colours. Then rearrange the cube until each face is a single colour.