Fodor's Expert Review Coster Diamonds

Even if you're not in the market for a new rock, the free, guided tour of (reportedly) the world's oldest diamond-polishing factory is certainly worthwhile. You'll learn all about the industry's "four Cs"—carat, color, clarity, and cut—and get to watch highly skilled diamond cutters plying their trade. There's also a replica of Coster's most famous cut: the Koh-I-Noor diamond, one of the prized gems of the British crown jewels.