Professor Stewart's Cabinet of Mathematical Curiosities

This book, written by Professor Ian Stewart, is possibly one of the best books I have ever read. Despite this, it has a format quite unlike an ordinary book; it has no coherent theme, and is full of tricky, and sometimes unsolved, math problems. When I first picked it up, I read the first few problems, and was about to set it down when I decided to flip just a few more pages ahead, and fell upon an essay about Fermat's last theorem.