King Gustav I began the castle in 1545 as a fortress to protect Stockholm. Reconstruction into a habitable castle started in the 1550s under Prince Magnus, Duke of Östergötland. The infobox gives completion in 1620 and names Arendt de Roy and Hans Fleming, though the article text does not. The style is Renaissance, and the article calls it one of Sweden's best-preserved examples.
Three stone buildings originally faced Lake Vättern, with three ramparts described as 31 meters wide, a moat and four round cannon turrets. The 19th century demolished the original ramparts, and the present ones opened in 1999. It was a royal palace until 1716, then a grain store.
The eastern half belongs to the National Archives, and the western halls are open to the public. The Vadstena Academy stages opera there each summer.
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