The island castle,^[1] or insular castle,^[2] is a variation of the water castle. It is distinguished by its location on an artificial or natural island. It is a typical lowland castle.

Because the island on which the castle was erected is separated from the shore by at least two bodies of water, artificial defences such as moats or shield walls were usually unnecessary if the castle was surrounded by flowing water. Such castles could therefore be very easily and cheaply built. Many island castles in lakes were, however, relatively easily captured in winter if there was an ice sheet thick enough to support attacking troops, because they were often rather poorly fortified.

• The best-known island castle in Germany is Pfalzgrafenstein Castle near Kaub, Rhineland-Palatinate
• The Chateau d'If is situated on the southern coast of France
• The English counterpart to Mont-Saint-Michel is St Michael's Mount in Cornwall
• Switzerland's iconic Chillon Castle sits on a small island on the eastern end of Lake Geneva
• The Aragonese Castle is situated in the Gulf of Naples
• The only water castle in Europe that utilizes Gothic architecture is Trakai Castle in Lithuania

Note: Mont-Saint-Michel in Normandy is not a castle as many people believe, it is a fortified monastery.^[3][4][5]

Though not entirely a castle, really consisting of a fort surrounding a palace, Murud-Janjira is a famous island fortress off the Indian coast in the Arabian Sea. The fortress is relatively unique in that the outermost defensive walls of the compound entirely encompass the island's natural land, thwarting any attacks using traditional amphibious landings.

• Castle

• Taylor, James (1889). The Great Historic Families of Scotland. Vol. 1. London: Virtue.
• Turnbull, Stephen (2003). Crusader Castles of the Teutonic Knights. Vol. 1: The Red-brick Castles of Prussia (1230-1466). Oxford: Osprey. ISBN 1-84176-557-0.