In Kleinmachnow, southwest of Berlin, a strictly secured complex of the Reich Post Research Institute was built on the Seeberg between 1939 and 1943. Here, Minister Wilhelm Ohnesorge had new weapon technologies developed for the Nazi regime, intended to win the war. At the same time, he expanded the adjacent residential castle, the Neue Hakeburg, built by the Wilhelmine court architect Bodo Ebhardt from 1906 to 1908, into his private residence. From 1947 to 1989, the SED used the area as the Karl Marx Party School, later as a district party school, and finally as a special school of the Central Committee. Hubert Faensen describes the eventful history of the listed complex from its inception to its current use as a school site, richly illustrated with rare historical photographs.