This is the best introduction to non-Euclidean geometry and special relativity that I have ever encountered. The book is basic enough to be understandable (at least to a degree) by any intelligent (and determined) adolescent, but deep enough for the physics or math undergraduate and perhaps even graduate student to find continual interest in. Rucker has a way of introducing complex ideas in a rather simple fashion so trhat one doesn't often realise how deep the subject matter is at first. Unlike some of his other books, however, considerable math background is required and a substantial amount of effort and force of will on the part of the reader will be necessary. All the same, the book is an intensely interesting foray into the world of geometry and relativistic physics. His adaption af Abbott's "A.Square" character to ealborated his ideas are particularly amusing and helpful.