The Trans-Siberian Railway Egg (1900)

This one commemorates an engineering feat with an engineering feat: open the egg and there's a miniature train, in gold and platinum, that actually runs -- five cars, diamond headlights, ruby taillights, wound by a key that folds flush into the egg itself when not in use. It's Faberge at its most literal-minded and its most impressive at the same time, turning the completion of the Trans-Siberian Railway into a piece of jewelry you could, in theory, wind up and watch move.