The Harderwykenburg is one of the oldest extant castle

Castle

A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...

s of East Frisia

East Frisia

East Frisia or Eastern Friesland is a coastal region in the northwest of the German federal state of Lower Saxony....

. It was built in the style of a medieval stone house soon after 1450 in Leer

Leer

Leer is a town in the district of Leer, the northwestern part of Lower Saxony, Germany. It is situated at the river Ems, near the border with the Netherlands....

, Lower Saxony

Lower Saxony

Lower Saxony is a German state situated in north-western Germany and is second in area and fourth in population among the sixteen states of Germany...

, Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

.

The original building, in the form of a tower, was built of stones from a monastery

Monastery

Monastery denotes the building, or complex of buildings, that houses a room reserved for prayer as well as the domestic quarters and workplace of monastics, whether monks or nuns, and whether living in community or alone .Monasteries may vary greatly in size – a small dwelling accommodating only...

, and measures 8.09 x 11.13 meters. The external walls are between 0.96 and 1.23 meters thick.
The tower was later supplemented by a two-storey extension. The steeply proportioned building has now been not entirely satisfactorily restored.

The first owner of the castle was probably the chieftain Hayo Unken, on his mother's side a grandchild of the chieftain Focko Ukena

Focko Ukena

Focko Ukena was an East Frisian chieftain who played an important part in the struggle between the Vetkopers and Schieringers in the provinces of Groningen and Friesland...

. The castle was also known as the "Unkenburg" , after Hayo's family name. In 1588 the steward (Drost) Dietrich Harderwyk Armgard married a daughter of Hayo Unken IV, and thus came into possession of the castle, which now bears his family name.

In 1788 possession of the building passed from the then owner, Carl Stephan von Schilling, to Carl Gustav, Baron zu Inn und Knyphausen, whose descendants continue to live there.