Stora Sundby castle was mentioned first time in Middle Ages. In 1364 it was besieged and captured by Albrecht during his battle with Magnus Eriksson. From the end of 1300s to the early 1400s it belonged to Lars Ulfsson Blå. After him Stora Sundby was owned by Julita monastery and families of Natt och Dag, Sparre and Chevron.
The present main house was built by Lars Siggesson Sparre, who asked Carl de Geer to design a new castle on the old Norman style. The casle was finished in 1848. The drawings were made up by the English architect J.F. Robinson. In refurbishment underwent castle a fundamental change in the exterior but the interior remained mainly unchanged. The architecture symbolizes a year calendar: 52 rooms (number of weeks per year), 12 small towers (12 months per year), four large towers (four seasons), 365 windows (days per year).
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.