The first documented mention of the castle was as Regensburg property in 1327. In 1355, Leutold II of Kuenring, the first known owner, died. The Kuenringers were a significant Austrian noble family, named after their seat Kühnring. Leutold's successors, Andre of Lichtenstein and Friedrich of Wallsee, renounced ownership for money, and Eberhard I of Kapellen acquired it in 1359. Subsequent owners included Ernst Preuhofer, the Liechtensteins, Chunrad the Steward, the Öders, Reinprecht V of Walsee, the Hausers, and Christof Zeller of Riedau, who were known as robber barons.
Georg von Wolframsdorf inherited it and around 1530, it passed to the Tannberg family, who sold it to Hans von Tschernembl in 1575. His son, Baron Georg Erasmus von Tschernembl, expanded it in 1608 with Antonio Canevale's design. As a Protestant leader, Georg left the country, and the castle was confiscated in 1620, bought by Count Leonhard Helfried von Meggau. During the Upper Austrian Peasants' War in 1626, the castle was briefly occupied. Later, it belonged to the Starhembergers, Kuefsteiners, and Thurnheim Counts, until 1899, when Baroness Therese von Schwitter owned it. In 1911, Count Alexander Hoyos acquired it, and it remains with his family. Archduchess Alicia, the last Grand Duchess of Tuscany, died there in 1935. After WWII, the Soviets renovated the Chinese Salon.
The castle, located north of Schwertberg where the Aist river exits the Josefstal valley, appears fortified with a design from 1608. Surrounded by the Aist on three sides, it has a Renaissance garden, one of the few of its kind in Austria, and a sundial on a round tower. The main building, partly Gothic and partly Renaissance, features arcades, a falcon kennel, and a chapel dedicated to Saint Mary. The Chinese Salon has wall paintings and a small Rococo library.
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.