Thorsager round church is the only one of its kind in Jutland (and one of Denmark's seven medieval round churches). It was built of brick around 1200 and is one of Jutland's oldest brick buildings - perhaps the oldest. Its thick walls (1m) are an indication of the defensive role it played.
The church may lie on the site of a pre-Christian sacrificial place for the god Thor. The size of the church and its architecture suggeste that is was built by an important man - probably the king. During restoration work in 1877-78 most of the church's outer walls were replaced with new bricks. Original bricks can still be seen in the north wall of the choir. During the last restoration in 1950-52 the beautiful church interior was restored with amongst other things a new altar and pulpit. There is access to the upper floor by a staircase within the door of the church.
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.