The island had been a residence since 1161, when Bishop Occo of Schleswig moved onto it after his own house was destroyed - though the oldest surviving structures date from the 13th century. After that it changed hands the way border property does. The Danish Duke of Schleswig bought it in 1268. In 1340 it went to the Schauenburg Count of Holstein at Rendsburg. In 1459, by maternal inheritance, it passed to Christian I of Denmark, the first Danish king of the House of Oldenburg. Each owner added to it, and the additions never quite agreed with one another: a medieval castle became a Renaissance fortress, and the Renaissance fortress became a Baroque palace, without any of them entirely erasing what came before. It sits on the Schlei, the long narrow inlet that runs some 40 km inland from the Baltic.

Frederick I, Christian's younger son, made Gottorf his principal residence and around 1530 had the west wing rebuilt in the Nordic early Renaissance manner. It was the first Renaissance building anywhere north of the Elbe - an architectural frontier crossed in a provincial duchy rather than a capital. The castle chapel followed in 1590, and in 1612 a private prayer box was fitted above the altar so that the ducal family could hear a service without being in the congregation. The chapel is one of the rooms where the building's layered centuries are easiest to read at a glance.

The court of Frederick III, who ruled from 1616 to 1659, turned Gottorf into a European cultural centre. Its most visible monument is the Neuwerkgarten, laid out from 1637 in the manner of Roman terrace gardens - a hillside stepped and levelled south of the castle, running down through terraces to a pond, with a figure of Hercules at its focus. The garden went the way of the dynasty. Its reconstruction did not begin until 1984, and the Hercules group was not put back until 1997, three and a half centuries after the duke first stood on his terrace and looked down the axis he had made.

In 1697 the Swedish architect Nicodemus Tessin the Younger began remodelling and enlarging the castle in the Baroque style. Only the vast south wing was finished. Duke Frederick IV was killed in battle before the rest could be built, and the great scheme stopped where it stood - which is why the courtyard still shows a Baroque facade on one side and older work on the others. The ducal line was forced out in 1702, and after Sweden's defeat in 1713 the Gottorp dukes were stripped of power by the Danish crown. Under Frederick IV of Denmark the palace slid into neglect. Furniture, paintings and fittings were carried off piece by piece, and in the 19th century the shell served as barracks, first Danish and then Prussian. After the war of 1848 the Danes ran a military hospital in it before converting it back to barracks.

In the last months of the war, in early 1945, Gottorf became a reception camp for people displaced from the eastern territories of the Reich, and it continued to house the displaced afterwards. Restoration began in 1947. From 1948 the buildings were handed to the state museums of Schleswig-Holstein, and the long repair of eight centuries of alteration was not considered finished until 1996. The castle now belongs to a foundation of the state and holds two collections: the State Museum of Art and Cultural History, and the State Archaeological Museum, whose holdings include the Iron Age bog finds from the Thorsberg moor a short distance north. The dukes who left in 1702 would recognise the building. They would not recognise what it is for.