The next step, like having a whole book of just Saturday Times crossword puzzles. Even more fiendish, even more fun, X-treme Sudoku proudly presents 320 puzzles rated "Difficult" to "Very Difficult." These are the toughest, knottiest, most demanding Sudoku out there—prepare to have your brain cells crackle, your pencils melt, your mind obsessed with numbers and squares. No one is better than Nikoli at rounding up such a collection. A Japanese puzzle and game company that started the Sudoku craze over twenty years ago, Nikoli is known for creating the only handcrafted puzzles around. As Tim Preston, publishing director of Puzzler Media, Britain's biggest seller of crossword and cryptogram puzzles, has said: "It is a matter of great pride to get your puzzle into one of Nikoli's magazines.