Sudoku: Extra Hard

Do you like to use your spare moments indulging in Sudoku? If so, Sudoku will be your perfect take-anywhere companion. With over 25 + puzzles guaranteed to sharpen your mind and keep you thoroughly entertained, this collection is a real treat for anyone who loves it is an extra easy Sudoku puzzle, Sudoku and more Sudoku. Are you ready to rise to the ultimate brain-training challenge?