Flatland: A Romance of Many Dimensions (1884)

A novella which is most likely to appeal to mathematicians and fans of social satire. It's set in a two-dimensional world, where women are lines and men are polygons. It explores the concepts of Victorian hierarchy and dimension through the visions and life of the narrator, a square. The first part of the story concentrates on 'Flatland' and its social aspects, and the second half revolves around the concepts of dimensions beyond what can be seen. Basically, a two-dimensional being cannot see past the dimensions it inhabits, and this rule also rings true for inhabitants of a one-dimensional existence ('Lineland'), a dimensionless existence ('Pointland'), and a three-dimensional existence ('Spaceland' or life as we see it). Obviously, since this book was first published, Einstein's theory of relativity brought to prominence the concept of a fourth dimension (time)...

It's much more interesting (and far less trippy) than I'm making it sound.