The Château de Lacassagne is thought to date from the latter half of the 15th century, with additions and alterations made in every century until the 19th century. It originated as an ancient salle (hall) and was altered in the 15th century with the addition of a spiral staircase and windows. A residence was added in the 17th century. On the first floor, in a room known as the Salle des Chevaliers de Malte, the painted decor was done between 1620 and 1640 for Jean Bertrand de Luppé, prior of St Gilles, and intended as a replica of the grand council hall of the Knights of St John of Malta. Among the pictures are copies of Matteo da Leccio's paintings representing the attack on Valletta by the Turks in 1565. The originals were in the council chamber of the Grandmaster's Palace in Valletta, Malta and were destroyed by Napoleon Bonaparte in 1798.
In the 19th century, a west wing was added to the main building. The castle is not open to the public.
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.