The small island of Saint Nicholas has an area of 150 acres
and belongs to the public and to the Municipality of Paxoi by more than 90%, while a small part of it is private, and another small part belongs to the monastery of Panagia, on the island located immediately after.
At the top of the island, at an altitude of 45 meters, lies the castle that, with permission from Venice, began to be built in 1423 by Baron Adam II San Ippolito, to protect the inhabitants from pirates. The permission was granted by the senate with a resolution on June 13, 1423 (Sathas Monumenta Historiae Hellenicae vol. III p.249). The year 1510 is engraved on the arch of the fortress gate as the completion date of its construction.
In 1484, the barony passed to the Venetian State, which then transferred it in 1513 for 3600 ducats to the Corfiot house of Ioannis Avramis. The taxation imposed by him on the people of Paxoi was so heavy that many families left the island and fled to Turkey and the uninhabited islands of the Othoni.
Initially, the fortress had a round shape, and its entrance was from the NE side, where the Kouviali mill was later built. It was reconstructed in its current form, at least regarding its exterior shape, in 1510 based on designs by Leonardo Da Vinci, as discovered in the archives of Venice by the architect and friend of Paxos, Roberto Veneri. Then, its size was reduced, and a platform was revealed in front of the gate, which was then moved to the NW side.
This platform must be a remnant of an ancient Greek structure of the castle. Parts of the ancient Greek wall, built with different materials and visibly older, are visible today. It seems that the Venetian conquerors of the island adopted the ancient Greek infrastructure as a base and extended or modified it as needed, following their resource-saving tactics applied in all their conquests.
Entering the perimeter of the fortress, the visitor encounters a wide courtyard surrounded by a low circular wall. To the left and right along the wall are the ruins of two-story buildings that served as barracks. Soldiers fired from the second floor against their enemies. In the center and to the left, there is a Venetian round cistern, and to the right, the newer English square cistern, from where the defenders of the castle got clean water. Opposite the entrance gate, there are three ramps leading to the small circular wall on which the Venetians pushed their huge cannons.