 Sandbjerg Estate, which had belonged for many years to the Dukes of Sønderborg, and then to the Reventlow family, was donated to Aarhus University in 1954.In addition, Sønderborg has a castle-like barracks built by the German military in 1906, placed centrally by Als Fjord, opposite Alsion (see picture below).The old part of Sønderborg is on the island of Als, but some of its western suburbs have spread onto the mainland of Jutland into what had been the interior of the fort of Dybbøl.