Bernegg Castle was built in the mid to late 13th century for the Freiherr von Calfreisen, though it was probably called Calfreisen Castle until the 15th century. A mention of Otto von Calfreisen in 1231 indicates that the family lived in the area before the castle was built. They may have lived in an earlier castle which was replaced in the mid 13th century or in the village. In 1259 and again in 1286 the Freiherr was mentioned in the castle. After the extinction of the Calfreisen family in the 14th century, the castle was acquired by the Unterwegen family. Hans von Underwegen was mentioned at the castle in 1386, though they may have acquired it earlier. In 1428 it was acquired by the Sprecher family, who changed the name to Bernegg. The castle then vanishes from the historical record until the mid 16th century when it was described as a ruin.
The castle ruin is located on a hill south of Calfreisen village. The palas is a rectangular building about 11 by 13 meters and four stories tall. The walls are 2.4–2 m thick at the base, tapering to 1.8 m on the upper levels. The ground floor probably served as the castle's cellar. The second story has several small arrow slits in the walls. One of the arrow slits on the south wall was expanded into a door way which now serves as the entrance into the castle. The original high entrance on the third story south wall is still intact. The remains of a brick oven can be seen on the fourth story.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.