Set near the Rijksmuseum, Coster Diamonds not only sells jewelry and loose diamonds but gives free demonstrations of diamond cutting so you can learn all about the "four Cs" -- carat, color, clarity, and cut. You can see a replica of the most famous diamond cut in the factory -- the Koh-I-Noor, one of the prize gems of the British crown jewels. After your tour, enjoy the petit café here.