Ortenburg castle was erected in the late 11th century by ministeriales of the Bavarian Prince-Bishops of Freising, who then held large possessions in the Duchy of Carinthia. Their descendants began to call themselves Counts of Ortenburg. The castle is located on the northern slope of the Gailtal Alps overlooking the Drava valley.
Damaged by the 1348 Friuli earthquake, the significance of the castle diminuished after the extinction of the Ortenburgs in 1418. The estates were inherited by Count Hermann II of Celje and in 1456 finally seized by the Imperial House of Habsburg. In 1524 the comital title passed to Gabriel von Salamanca, who had his new residence, Porcia castle built in the nearby town of Spittal an der Drau.References:
Ängsö Castle was first named as "Engsev" in a royal charter by king Canute I of Sweden (r. 1167-1196), in which he stated that he had inherited the property after his father Eric IX of Sweden. Until 1272, it was owned by the Riseberga Abbey, and then taken over by Gregers Birgersson.
From 1475 until 1710, it was owned by the Sparre family. The current castle was built as a fortress by riksråd Bengt Fadersson Sparre in the 1480s. In 1522, Ängsö Castle was taken after a siege by king Gustav Vasa, since its owner, Fadersson's son Knut Bengtsson, sided with Christian II of Denmark. However, in 1538 it was given by the king to Bengtsson's daughter Hillevi Knutsdotter, who was married to Arvid Trolle.
In 1710, the castle was taken over by Carl Piper and Christina Piper. Ängsö Castle was owned by the Piper family from 1710 until 1971, and is now owned by the Westmanna foundation. The castle building itself was made into a museum in 1959 and was made a listed building in 1965. It is currently opened to visitors during the summers.
The castle is a cubical building in four stores made by stone and bricks. The lower parts is preserved from the middle ages. It was redecorated and expanded in the 1630s. The 4th storey as well as the roof is from the expansion of Carl Hårleman from 1740-41. It gained its current appearance in the 1740s.