Flatland: A Romance of Many Dimensions by Edwin A. Abbott is a nice little book. Abbott blends planar geometry and reality brilliantly. For example, every planar geometry object is a member of the flatland and as the number of points grow in the figure it becomes more wise; Circle is the wisest of all. It's funny how he describes personality types using isosceles triangles, equilateral triangles, and squares. In fact, he calls himself a square.

Be warned for sexist ideas and satirical writing.