What makes this the world's most difficult coloring book? This is an art book as well as a grayscale coloring book. The images are dreamlike and complex enough to be enjoyed as illustrations. Many of the images warp into the background or change into other shapes which make this a unique challenge for the colorist. The images may also form to make up larger images, enhancing the difficulty. Even I, using marker and color pencils, have stumbled upon forgotten parts of the piece realizing it melted into something different. It is definitely unique. Whether you enjoy this book simply for the illustrations, or want the bragging rights to say you completed the 'world's most difficult coloring book', or as a gift, here is what you can look forward to... Over 50 Pages of illustrations in varying ranges of light and dark contrast. These are grayscale images, not traditional black and white line art coloring pages. Some of the images may be too intense for younger children.