Trakai Peninsula Castle is one of the castles in Trakai, Lithuania. It is located on a peninsula between southern Lake Galvė and Lake Luka. Built around 1350–1377 by Kęstutis, Duke of Trakai, it was an important defensive structure protecting Trakai and Vilnius, capital of the Grand Duchy of Lithuania, against attacks of the Teutonic Knights. Much of the castle was destroyed in the 17th century.