Castle Rushen (Manx: Cashtal Rushen) is a medieval castle located in Castletown in the south of the Isle of Man. It towers over the Market Square to the south-east and the harbour to the north-east.
The castle was built to protect the entrance to the Silverburn River and was gradually developed between the 13th and 16th century. King Magnus III, the last Norse ruler of Mann and the Isles, founded Castle Rushen sometime around 1250 and the Norse Sudreyan Royal House used it as their residence until the 1266 Scottish take-over. Today, it is run as a museum by Manx National Heritage, depicting the history of the Kings and Lords of Mann.