Here's an interesting little mathematical curiosity called the Szilassi polyhedron. Topologically, it's a torus, but made from only 7 flat pieces. Each surface is a different colour and has 6 edges. Every face shares an edge with all 6 other faces, proving that a minimum of 7 colours are necessary when mapping on a torus. The print is in full-colour sandstone and in spite of its tiny size and low price, has come out remarkably well. You can find it in the microcubology shop here.