Tretower Castle is a Grade I-listed ruined castle in the village of Tretower. It was founded as a motte and bailey castle by Picard, a follower of Bernard de Neufmarché. Probably around 1150, Picard's son, Roger Picard I, replaced the motte with a shell keep. By about 1230 a tall cylindrical keep was added to the inside of the shell keep, possibly by his great-grandson, Roger Picard II, and the space between was roofed over. At this time the earlier bailey was walled in stone and provided with cylindrical corner towers. In the early 14th century residential buildings were constructed away from the original fortifications forming today's Tretower Court. Over time the lords of Tretower favoured the more luxurious Court and the castle fell into disuse.
The castle is roughly triangular in plan, with the motte and keep assemblage occupying the western corner. The 12th century shell-keep is an irregular enclosure with a gate-tower on the line of approach from the bailey. In the centre of the shell stands the tall cylindrical 13th century keep. The keep is of three storeys, with an original entrance at first floor level, above a strong, slanted batter or talus. The top of the talus is marked by a decorative string-course of stone.
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.