With its 9 x 9 grid, this number puzzle presents the biggest challenge beyond the Rubik's Cube. The empty spaces must be filled so that the numbers from 1 to 9 appear only once in each row, each column, and each 3 x 3 block. And the best part: you don't need to be a math genius or a fan of numbers to love Sudoku. It features 5 difficulty levels. This unit includes 5 simultaneous titles.