Illingen Castle was documented first time in 1359 when it was owned by Dietrich V. von Kerpen (this is why castle is also called Kerpen Castle). In the16th century it was moved to the hands of Nassau-Saarbrücken counts, who owned Illigen until French Revolution. Illingen castle was badly damaged in the Thirty Years' War and rebuilt later.
The castle started to decay after 1825 and was used as a quarry. The tower was restored in 1951 and today there is a restaurant.
The Royal Palace was built in the first half of the 19th century as the Norwegian residence of King Charles III, who also reigned as king of Sweden and otherwise resided there, and is the official residence of the present Norwegian monarch. The crown prince resides at Skaugum in Asker west of Oslo. The palace has 173 rooms.
Until the completion of the Royal Palace, Norwegian royalty resided in Paleet, the magnificent town house in Christiania that the wealthy merchant Bernt Anker bequeathed to the State in 1805 to be used as a royal residence. During the last years of the union with Denmark it was used by the viceroys of Norway, and in 1814 by the first king of independent Norway, Christian Frederick.