The Ducey domain came into the hands of the old Norman Montgommery family in 1521 after the wedding of James Montgommery to Claude de la Boissière, the heiress to the lands of Ducey. The castle was built at the beginning of the 17th century by Gabriel II de Montgommery, one of the sons of Montgommery first who became famous for killing Henry II, king of France, by accident in a tournament on 30th June 1559. He converted to Protestantism and became one of the greatest Protestant Chiefs in the area. Gabriel caused the hatred of Catherine de Medicis and was beheaded on the Place des Grèves on 26 th June 1574. Gabriel II de Montgommery was born in 1565 an inherited the lands of Ducey. Following his father's example, he became the chief of the Protestants in the Avranches area.
Today Château des Montgommery is open to the public.
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.