Blankenhagen Castle — Wikipedia

Blankenhagen Castle (German: Burg Blankenhagen) was a lowland castle (Niederungsburg), whose ruins are located by the River Aller near Grethem in Lower Saxony, Germany. The motte-and-bailey castle is believed to have been built around 1200. It is supposed that there used to be fortified buildings on the two low mounds or mottes, and that a bailey was constructed on an outer island-like area.