On their own, the paper sculptures are intriguing to look at, let alone think about. Each is a collection of shapes: full of color, sized differently, attached to each other in very original ways, and otherwise engineered to invite the reader into its complicated world. Then the reader is challenged to lift the book, "turn it around and view it from every angle." Questions are asked, many with no singular answer, and they force the participant to look again and definitely "think outside the box."

Besides designing such mental challenges as this, Ron van der Meer teaches children math and makes it fun. He has also published over 150 books and is known as a "pioneer of the modern pop-up." This spectacular book is the one he thinks is his best.

Find out more about the history of pop-up books and check your answers to the challenges with the book's Web site.