Summary
Edwin Abbott's Flatland (written under the psuedonym A. Square) is among the most entertaining and thought-provoking explorations into the nature of space and the universe.
Abbott, an English schoolmaster and theologian, published under the psuedonym A. Square out of fear that he would face mockery from the mathematical community and disdain from his religious colleagues.
Text
The entire text of Flatland is in free domain, and can be found
here.
Illustrations
One of Abbott's strengths was his simple yet imaginative style of illustration. As an example, here is his illustration of a typical Flatland dwelling:
