Hardegg Castle was first mentioned in an 1145 deed, it was acquired by the Counts of Plain about 1187. Hardegg itself is first documented as a town in 1290. Located on the border with the Kingdom of Bohemia, the area was devastated during the Hussite Wars in 1425. In 1483 Hardegg was bequeathed to the Habsburg archdukes of Austria.
Emperor Maximilian I granted Hardegg to his ministeriales of the Prueschenk noble family and elevated them to immediate Counts of Hardegg in 1499. Two years later Count Ulrich purchased the Bohemian County of Kladsko from the Dukes of Münsterberg. From the Thirty Years' War onwards the castle decayed, until it was acquired by the Khevenhüller dynasty and rebuilt in the late 19th century according to plans designed by Carl Gangolf Kayser.
After World War II until the fall of the Iron Curtain, Hardegg was particularly isolated. The only connection to the Czech Republic is via a bridge built in 1874 across the Thaya to the neighbouring village of Čížov.
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.