Caltavuturo Castle clings to the top of the hill called Terravecchia, overlooking the modern small town to the north. It was originally the city's medieval core, completely abandoned for a different site (that of the modern town) only in modern times. The origins date from the Arab period.
Some massive parts of the walls remain, being a curtain wall of quadrangular plan and another semi-cylindrical tower to protect the access on the north side.
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.