Rubik's Cube 4x4

The Rubik's Cube 4x4 (also known as the Revenge or the Master Cube) is a 4x4x4 version of the Rubik's Cube.
Unlike the original Rubik’s Cube 3x3 (and the Rubik’s Cube 5x5), it has no fixed facets: the centre facets (four per face) are free to move to various positions. This innovative design makes the 4x4 much more challenging, slicker, faster and more robust – A True Master Cube.