Trakai Island Castle is an island castle located in Trakai, Lithuania on an island in Lake Galvė. The construction of the stone castle was begun in the 14th century by Kęstutis, and around 1409 major works were completed by his son Vytautas the Great, who died in this castle in 1430. Trakai was one of the main centers of the Grand Duchy of Lithuania and the castle held great strategic importance.