The first document explicitly mentioning the Castle of Cancellara dates back to the 15th century. During that period, the feudal property belonged to King Ferdinand I of Naples, also known as Ferrante, and his son Frederick I of Naples. Before this date, some documents testify to the existence of the fiefdom and the settlement of Cancellara, although they do not explicitly refer to the castle.
The devastating earthquake of 1694 caused significant damage and left it in ruins. In 1806, it was partially used as a prison. In the following decades, the fortress, upon which it was built, suffered landslides, floods, and earthquakes.
The castle, constructed from limestone, spans three levels and consists of various buildings around two inner courtyards. The castle still retains architectural elements typical of medieval fortifications that evolved in response to social changes and housing needs. The original keep, likely built by the Normans, saw the addition of the castle/residence of the feudal lord during the 15th century. It was later transformed between the 16th and 18th centuries, first into a baronial palace, then divided, and finally repurposed as a prison, school, and private residence in the 19th and 20th centuries.
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.