When the Peninsular castle was being built, fortified and expanded - at the second half of the 14th century - the Island Castle was begun to be build on one larger island of Galve Lake. At the first stage of building works the Island Castle was of an in-between type – either fenced or conventional – it was of U form and had duke palace and ante palace. It is thoughts that Island Castle was begun by Kestutis and finished in the early 15th century by his son Vytautas. It was meant to be a fortress and it was never conquered by any raiders.
At the second stage of building works the layout of the castle was a little changed: between the two castle blocks a 9,2 x 9,6 m large and 6 floors height donjon was constructed (33 meters), and at the edge of the island a defensive wall with counterforts was built. The architecture style of the Castle is Gothic but separate elements were of Romanesque style. All the rooms were arced, window slots were decorated with trimmed bricked. On the second floor of the right block there was a representative chamber; windows were decorated with stained-glass. About the architecture of the Island and Peninsular Castles there was for the first time mentioned by a Fleming traveller Giliber de Launa, indicating that “the second Castle is in the middle of the lake in a distance of a cannon shoot form the first Castle. It is completely new and is built from brick according the French example.” At the last stage of the building works a fossa was pitched, separating duke castle from the ante-castle, it is hedged with a defensive wall with towers, there were casemates built. In the southern and triangular casemates there were kitchens, on the lower floors of the western casemates there were stockrooms, and on the second floor of casemates servants lived. In the southwest tower if the Castle there was a prison. The ante-castle gained a form of irregular trapezium, in the Eve of the Battle of Grunwald the Castle was expanded and renewed; the angle towers were readjusted for the flank defence and had 15 cannons. After the Battle of Grunwald (in 1410), having defeated the Teutonic Order the Island Castle became the residence of the Grand Duke. In the beginning of the 15th century Trakai was a flowering town, frequently visited by merchants, honoured guests, foreign messengers, who were welcomed in the representative chamber of the Island Castle. In 1413 in the Island Castle there was welcomed the Emperor Zigmantas’s messenger Benedict Macra, who was assigned an arbiter in the argument with the Order on the border with Samogitia. The Polish King Jogaila (Vytautas’s cousin) came with a visit for 13 times.
In the 16th century after having lost the military and residential functions the role of the Castle went down and the Grand Dukes visited it more and more seldom. The Metrics that was kept in the Castle was moved to Vilnius in 1511. The Island Castle becomes a prison for noble criminals.
After desolating invasion of the Tsarist Russia in 1655 – 1661 Trakai town was plundered and burned, the Island Castle was destroyed and was not rebuilt; the town never revived and became a province.
In the 19th century Romanticism ideas lead to show interest in Lithuanian past, especially Trakai Castles. Artists painted the ruins of the Island Castle, the remained fragments of the frescoes, the engineers – architects prepared the restoration projects for the castle. Engineer B.Malevskis prepared a project for fragmentary and conservational works in the ante-castle west-east tower. Although the works accomplished were not large, in the history of castle preservation they were very important. In 1929 – 1941 the restoration works were supervised by a Polish architect J.Borovskis. In that period the sole of the stonework was consolidated, the corner counterforts were restored/renewed, the remains of the ruin were removed form the fa?ade, the donjon was fortified, the representative chamber was began to be reconstructed.
After the World War II the conservational, restoration and reconstructional works were continued by Lithuanian restaurateurs. In 1953 the reconstructional works of the Castle started. In 1962, following the project of architect B.Kruminis the central palace were rebuilt, and in 1987, following the architect St.Mikulionis the anti-castle was rebuilt. The corner towers of the anti-castle were also rebuilt and the western casemates transformed the whole volume/size of the dimensional composition of the Castle. The symbol of Lithuanian and of town Trakai – the Island Castle – regained its previous outlook as it was in the 15th century. After the re-establishment of Lithuanian Independence Trakai Island Castle again welcomes honoured Lithuanian guests; it also is a place where important contracts are signed.
In 1962 the Island Castle was conveyed to Trakai History Museum. Many expositions were installed since then, many exhibitions are now open to the visitors, and numerous exciting concerts, festivals and holiday events take place in the Island Castle in the present days.