The number of European heads of state who still live in actual castles is vanishingly small—much like the principality of Liechtenstein itself. This tiny country, about 62 square miles, the same size as Washington D.C., is ruled over by the Prince of Liechtenstein, whose family has lived in Vaduz Castle off and on—currently on—for roughly 400 years. The schloss (German for “castle”) sits on an alpine hillside above the town of Vaduz, the country’s capital and largest city, and can be seen from every location in town. While the interior…