Recursion: The Art and Ideas Behind M. C. Escher’s Drawings

That is a kinda boring link, but here's a high-quality (and dramatic!) exposition I encountered recently about Escher's correspondence with Coxeter and the method by which one might construct figures like his Circle Limits without a computer. If you're further intrigued, there are more related links at the bottom.

http://www.ams.org/samplings/feature-column/fcarc-circle-lim...

Very much relevant to anybody who found this interesting: http://www.amazon.com/Godel-Escher-Bach-Eternal-Golden/dp/04...

I found it in a used bookstore for $5 once, totally by accident. It's probably the best nonfiction book I've ever started (I unfortunately never bothered to finish, which isn't so good. It's still in my backpack in case I ever get stuck anywhere...).