Maasi medieval fort-castle was built with the forced labour of islanders. That's how the ruling Liivi order punished indigenous inhabitants for the uprising, which had destroyed orders previous stronghold. Seaside fort-castle was undefeated until destroyed by Danes. The fortress was blown up in 1576 by the Danes in an attempt to forestall the Swedish invasion and nothing was done for the next 300 years. 8m walls that survived the destruction have become a landmark.
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.