Montfort Castle was built by the Counts of Veldenz around the year 1200. The first known dweller at the castle was Eberhard von Lautern (1182-1240). Lautern family owned the castle until 1432. In 1456 the army of archbishop of Mainz and Elector Palatine Frederick I destroyed the castle in local feud.
Despite some repairs Montfort stayed ruined several centuries until the remains where repaired in the 20th century. Today the castle can be visited free. There is also a small museum.
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.