Felsenburg castle was probably built in the 12th century for the Freiherr of Kien. The castle was built on a rocky spire above the road over the Gemmi pass into Valais. It was inherited, along with the rest of the Herrschaft of Frutigen, by the Freiherr of Wädenswil in 1290. The Freiherr of Turn acquired it from Wädenswil in 1312. It was mentioned in a record in 1339 as the castrum de Petra. It was again mentioned in 1368 as Stein, German for Stone. In 1400, Bern acquired the castle along with the rest of the Herrschaft. They abandoned Felsenburg and allowed it fall into ruin.
Currently, only the rectangular main tower and remnants of the outer walls are still standing.
References: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.