… and this “World’s Most Challenging Puzzle” results. The 36 Cube is available from ThinkGeek, who likens it to a 3D Sudoku puzzle. The game was developed by Dr. Derrick Niederman of MIT and is based on Euler’s 36-officers problem. The goal is to place the colored pieces so that each color appears only once in each row/column and the ending arrangement must result in a perfectly smooth cube. It would make a great holiday gift for the puzzle lover in your life. It’s $19.99 at ThinkGeek.