This one is right up there with Alan Lightman's 'Einstein's Dreams' (further up on the list). How would the world appear to you if it had but two dimensions? How about one dimension? That's what the Square has to deal with when he visits Lineland. Or no dimensions at all(in Pointland). He's transported to Sphereland, which is where we live, and is astonished to find this third dimension. He then speculates on a fourth dimension, which the Sphere tells him is ludicrous, which is the point of this fairy tale. It's difficult for people to imagine things beyond the range of your sensations. This book will have you doing that, though. A quick read and well worth your time.