Hard Sudoku 16 X 16 Puzzles: Volume 3 (16 X 16 Sudoku Puzzle Books For Adults)

Uses letters and numbers and are big sudokus.enjoyable and need conentration

I buy one of these for my wife every year and she loves them. Very difficult and challenging. Just like living with me.

So goodI get lost in these for hours

Really hard!

I am mad about this book although not for the faint hearted as it is extremely difficult. Wasting many hours on them but be lost without it over my morning coffee