Extra tricky. Extra tough.
It's the sudoku collection that's not for the faint of heart. If you're craving the challenge, sharpen your pencil and pit your wits against the Japanese puzzle-makers at the top of their game. In each of these more than 300 handcrafted puzzles, ranked by difficulty from expert to x-treme to ultimate, every move is an adventure, a one-on-one challenge with a grandmaster who delights in elegance, symmetry, and building in the occasional roadblock. But keep going. You'll solve it eventually... you genius!