The earliest traces of human settlement on the Sulzbach castle hill have been dated to the Late Hallstatt or Early La Tène culture. The medieval settlement was built first in the 8th century or early 9th century. The partially stone-made castle was built there in the 9th or 10th century. In 1003 the castle was moved to the Nordgaugrafen family by Henry II. The medieval castle was rebuilt from 1618 to the Renaissance style. Today the original tower from c. 1100 exists.
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.