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:Herceg Novi was founded (on a former small fishing village, existing since Roman Empire times) as a fortress in 1382 by first Bosnian King Stjepan Tvrtko I and was called Sveti Stefan or Castelnuovo. The Turks conquered Herceg Novi in 1482, and ruled for 200 years, until 1687. However, there was a short pause between 1538 and 1539 when it was held by the Spaniards before they were defeated in the Siege of Castelnuovo. Turkey ruled again until 1687, from then until 1797, the town was ruled by the Venetian Republic.
The Herceg Novi old town is amazing. It is on a fairly steep hill that leads all the way down to the sea. Wandering through the small stairways to the various plazas and fortresses is a many hour adventure.