First mentioned as Soban, Sobień Castle was a Royal castle guarding the merchant route along the San River. The castle was built by order of King Casimir the Great in 1340. In 1389 Władysław II Jagiełło conferred the castle to a noble family of Kmita.
The castle was destroyed in 1474 and again in 1512 by Hungarian forces. In 16th century the Kmita family sold the estates and the castle to Stadnicki family, who held it until 1713.
References: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.