The keep of Crupet Castle was built in the 13th century and originally consisted of a square tower surrounded by a moat. The entrance was probably protected by a drawbridge and portcullis. In the 16th century, the keep was converted to a manor house. A corner tower was added, the windows were enlarged, and the timber top floor and roof were built. The drawbridge was probably also replaced at this time. The keep is not open for visits, but is highly visible from the surrounding roads.
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.