Brain Twisters Sudoku Challenge Vol 2: Extreme Sudoku Puzzles EditionPaperback, 3 March 2016

Playing Sudoku is a calming experience that you definitely must try. It is a relaxing tool that will not take much of your time at all. You don't have to go somewhere else just to play and be relaxed. Instead, you can just pull out a copy and play right away! Create your own haven wherever you are. Bring this Sudoku book anywhere you go!