The Gardiki castle is situated at the southern part of the island. It was probably constructed during the 13th century. During the Venetian rule (1386-1797) the castle was abandoned. The fortification circuit is elliptical in plan, has a perimeter of 332 m. and encloses a total area of 5.165,70 m2. At regular intervals there are eight two storey quadrilateral towers with arrowslits. Apart from the tower of the main entrance, there are also gates at three other towers. Towers had access to the interior of the castle by means of two superposed openings. Fresco remains in the first floor of a tower indicate its use as a chapel. The circuit walls and the towers were crenellated. Stone built staircases, two of which survive to this day, led to the battlements. On the rocky interior of the castle no buildings have been detected other than a kiln, probably for lime production.
The castle is constructed of rubble masonry with broken tiles. Specific parts include ashlar masonry and massive ancient blocks in secondary use. Of particular interest is the masonry of two towers which involves horizontal brick courses, blind arches and niches over the lintels of the openings. During recent research there was recovered evidence for the use of the area as burial ground since 6th century BC until Late Roman to Early Christian antiquity.