Palace Museum (Schlossmuseum Darmstadt)

One family tree here runs straight through European history. Queen Victoria's daughter Alice became grand duchess of Hesse, and her daughter Alix married Nicholas II and became the last empress of Russia. Two generations later the house was tied back to Britain when Cecilie, a sister of Prince Philip, married the Hessian heir. For a modest residence in a mid-sized German city, that is a remarkable amount of European history in one building.