Trakai Island Castle is located in Trakai, Lithuania on an island in Lake Galve.  Construction was begun in the 14th century by Kestutis, and around 1409 major work was completed by his son Vytautas the Great, who turned the castle into an unassailable fortress which has never been conquered by enemies.  Trakai (30 km from Vilnius) was the ancient capital of Lithuania and the castle held great strategic importance. 

It is an excellent example of Gothic architecture, surrounded by thick defensive walls and protected by the fore-castle with 3 major towers on the corners.  The top story of the towers was designed for soldiers and housed a large number of cannons.  The southwestern tower was also used as a prison.

The first attempts at restoration in the 19th century practically ruined the castle.  The main restoration works were conducted during the time of the Soviet occupation.  From 1962 the castle has housed the Trakai History Museum.