Lucens Castle's strategic location allowed it to control the Broye valley, which was an important transit corridor. Starting in the Middle Ages and until 1536 it was a residence of the Bishop of Lausanne and served to control the Bishop's land in the Broye valley. During the 12th century, the castle was repeatedly destroyed and rebuilt. In 1476, it was destroyed by the Swiss Confederation. In 1536 the valley and the surrounding territory were conquered by Bern. It became the seat of a Bernese bailiwick at the same time. In 1542, the vogt of Moudon moved into the castle.
The castle was enlarged between 1579–86 and served as an arsenal and fortress on the border to Fribourg. In 1798, the Bernese were forced out and the Canton of Léman was formed. Shortly thereafter, the castle became the property of Canton, who sold it 1801 to private individuals. In 1925, it was converted into a Swiss Reformed institute for girls. Between 1965-70, it was the seat of the Conan Doyle Foundation, and is now in private hands.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.