What Book's Artwork Added The Most To The Story?

Whether you want to talk up J.R.R. Tolkien's cartography skills or you're a fan of Maurice Sendak's imaginary beasts, tell us what book had the visualizations that were most pivotal to your imagining of the story.

Tell us in the comments which the book is your pick and what it was about the illustrations -—whether it helped you to understand just what was going on or simply added to your own imagination — that made the illustrations so unforgettable. Pictures or links to the art, too, please!

Image: Draft sketches from The Little Prince via Open Culture.