The Hard to Extreme Sudoku Puzzle Book (Volume 1) Sudoku is not only a placement game that brings us lots of fun, but also a great brain exercise that helps strengthen our mind and boost memory. In this compact size book, you can play 120 large-print sudoku puzzles with increasing complexity level: 30 hard puzzles, 30 a bit harder puzzles, 30 much harder puzzles, and 30 extreme puzzles. This is a great gift for anyone who loves challenging sudoku puzzles, especially those with eyesight problems.