The Manningaburg castle in Pewsum dates back to the year 1458 and was originally - as the name suggests - the headquarters of the chief family Manninga. However, in 1565 the castle was sold from Chief Haiko Manninga to Count Edzard II Cirksenas. Unlike most castles in Ostfriesland, Manningaburg is open to the public and houses a museum dedicated to the chief and castle history. In the ceremonial hall of the castle, you can get married in a civil ceremony.
References:Duino Castle was built by the Wallsee family in 1389 on the cliffs overlooking the Gulf of Trieste. It replaced an older castle from the 11th century. Over time, the Wallsee family disappeared and the castle, after having been used as a prison, became the residence of the Luogar and Hofer.
At the end of the 19th century it became the property of Prince Alexander von Thurn und Taxis from the Czech branch of the House of Thurn and Taxis. It remains with the family to this day with his great-grandson Prince Carlo Alessandro della Torre e Tasso, Duke of Castel Duino the current owner. The castle has been opened to the public as a museum and park.