M.C. Escher is a phenomenon. He is the rare artist whose work seems to have skipped the museums and gone straight into pop culture. Indeed, one is more likely to see his drawings in a college dorm room or on some geeky kid's tshirt than at a gallery. And, yet, he is respected by not only the artistic community but also by the mathematical and scientific community. Escher truly is a phenomenon.
People are so drawn to Escher's later designs because they are so baffling. Every piece fits together and yet each piece is identical. As Bruno Ernst put it, his designs are "jigsaw puzzles with identical pieces." One can begin to comprehend the actions that Escher went through in creating his pieces by understanding the math behind them.
In particular, Escher exploited different types of symmetry through tesselation.