Opposite Gaiοs is the tree-lined island of St. Nicholas with the homonym castle standing on the top. The well- preserved castle,  whose construction began in 1423 and was completed based on drawings by Leonardo da Vinci in the middle of 1500’s.
Visitors going up the well- walked path can enjoy the view of the picturesque  Gaios and tour at the top the most important points of the castle namely  the Venetian and English tank, the observatory, the so-called “Gouardiola”, the cannons and the remaining barracks lacking the roof.