THE MOST COMPLEX CUBE: One of the largest Rubik’s Cubes created, the 5x5 promises to push your problem-solving capacity. Known as the Professor Cube due to the sheer difficulty to complete it!,THE ULTIMATE CUBE TEST: The Rubik’s 5x5 is not for the faint-hearted and is the most complex of all the Rubik’s Cubes. For Ages 8 and up. WARNING: CHOKING HAZARD - Small Parts. Not for children under 3yrs.