When you buy this book you get an electronic version (PDF file) of the interior of this book. Hidoku is a fun and addicting logic puzzle game. It is very similar to Numbricks. The goal of Hidoku is to fill in the missing numbers, in sequential order, going horizontally, vertically and diagonally. Unlike Numbricks, diagonal paths are allowed. This book is ideal for you if you love to solve difficult and huge Hidoku puzzles. You do not need to wade through tons of easy Hidoku puzzles before getting to the real brain teasers. You will experience Hidoku 20x20, Hidoku 25x25 and Hidoku 30x30. You get the perfect mix of different sizes of Hidoku to keep you entertained for weeks. Once you pick up this book, you won't be able to put it back down. You have been warned! Only 1 Hidoku puzzle per page, with lots of white space for scribbling. Hidoku Mixed Grids - Hard is a collection of 156 puzzles: 42 hard Hidoku 20x20 puzzles 42 hard Hidoku 25x25 puzzles 42 hard Hidoku 30x30 puzzles 30 extra logic puzzles I guarantee that every logic puzzle in this Hidoku puzzle book has been carefully checked to ensure that each puzzle has only 1 solution. None of the puzzles in this book will appear in any of the other PuzzleBooks.net books. Hidoku is also known as Number Snake.