I've been enjoying listening to Professor Roger Penrose talking about aspects of his work on YouTube. Not only is he a very clever guy, he's also a good presenter. He's done an amazing amount of interesting and important work in mathematics and physics and is well known for his expertise in exotic things like Black Holes. I remember buying a book of his years ago called The Emperor's New Mind, in which he theorises on the nature of consciousness and its links to quantum mechanics. In book form, over my head; but in talk form, much more accessible.
Penrose saw work by the great Dutch artist M C Escher at an exhibition in Amsterdam in 1954. Struck by how ingenious Escher's "impossible" drawings were, he invented some "impossible" stairs with his father, Lionel Penrose. From a picture on Wikipedia :
Escher loved this and incorporated the idea in a famous drawing of his called Ascending and Descending :
Here's some Penrose :