Unlike classic Sudoku, Sudoku 16x16 (also called hexadoku) is based on a 16x16 grid, and the object is to place the numbers 1 to 16 in the empty squares so that each row, each column, and each 4x4 box contains the same number only once.
There are 100 hard puzzles in this book.
Due to the large grid and the difficulty level, this book is a real challenge even for Sudoku experts.