The Times Samurai Su Doku 13: 100 Extreme Puzzles for the Fearless Su Doku Warrior (Paperback) (ISBN-13: 9780008673130)

For anyone who loves the challenge of Su Doku but manages to solve them within minutes, you can now enjoy the extended mental workout and ultimate endurance test of a five grid interlinked system.

This is Su Doku multiplied: every column, row and 3x3 box must contain the digits 1 to 9. Where the puzzles overlap, the rows and columns do not go beyond their usual 9x9 length but the interlocking boxes give you more clues - and more complexity.

With another 100 new Samurai puzzles to vex you for hours, lose yourself in the four levels of this book:

10 Easy
40 Mild
40 Difficult
10 Super difficult

Even the speediest of Su Doku solvers will be agonizing over these ultra-complex, extended brainteasers.

These are the most difficult Su Doku puzzles in The Times range.