Leuchtenberg Castle was built around 1300 by the landgraves of Leuchtenberg, an influential medieval aristocratic family. Presumably there was already a fortification on the hill before. The noble family died in 1646. After the death of the last landgrave, the castle deteriorated rapidly, in 1842 it was completely destroyed in a major fire.
In the 20th century the castle ruins wer restored and today it is used as an open-air stage and is the venue of the annual castle festival Leuchtenberg.
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.