Greinburg Castle was built between 1488 and 1495 by Heinrich and Siegmund Prüschenk with the imperial approval of Emperor Friedrich III. In 1533 Johann Leble (Löbl), acquired the castle. Under him the building received most of its present day form. In 1621 the castle was sold to the Earl Leonhard Helfrich of Meggau, who carried out basic changes. A three storeyed, columned arcade became the main feature for the appearance of the inner courtyard. Furthermore, under Meggau the Sala terrena (so-called stone theatre) was installed. In 1625 the “Rittersaal”, the Hall of Knights, and an adjoining chapel in the south west tower were redecorated.
The Dukes of Saxe-Coburg and Gotha have been owners of the Castle only since 1822. The building, which comprises four wings, houses the Coburg Rooms, which are the official rooms of the ducal family, as well as the Upper Austrian shipping museum.
Towering 52 meters above the sea, Bengtskär lighthouse is the tallest one in Scandinavia. The building started in in 1905 after the shipwreck of S/S Helsingfors and was completed in 1906. The lighthouse was designed by architect Florentin Granholm. On December a special petrol lantern, designed and built in Paris, was brought to Bengtskär and installed atop the tower.
German fleet bombarded Bengstkär in the First World War in 1914. Since the Gulf of Finland was heavily mined, it was not until 1919 that the surrounding seas were declared safe for shipping, that the light was lit again.
After the war the military value of Bengtskär increased as part of the defence system of independent Finland. In Second World War (1941) Soviet Union made a suprise attack to island. After a bloody battle, the small Finnish garrison emerged victorious. Intermittent repairs to the facility continued during the post-war period.