EVEN IN A city strewn with such a wealth of abandoned architectural oddities, Schloß Dammsmühle stands out as remarkable—both for its age (the main building is nearly 250 years old) and the remarkable (and infamous) pedigrees of some of its 20th-century owners. Built in 1768, it was alternately improved and abandoned through the Weimar era before being commandeered by the Nazis, and in 1940, Himmler made it his base of operations.