The castle was built on the steep rise of the islet Imeri Gramvousa, at the edge of the homonymous peninsula, to protect the small natural port that exists in the area, in the framework of a wider fortification project of Crete at the end of the Venetian rule.
Its construction started in 1584 with the designs and the supervision of Latino Orsini. The shape of the fortress is irregular, with walls and bastions on three of its sides, while in the north it is protected by inaccessible rocks. The protected gate is on the eastern side and leads through a vaulted “stoa” to the inside of the fortress.
The castle covered an extensive area and included underground reservoirs that collected the rain water, foundations of buildings, the church of the Annunciation and the gunpowder warehouse, which was transformed into a mosque during the Ottoman rule. The fortress was occupied by the Ottomans in 1692 because of treason and remained in their possession until the Revolution of 1821, when it was occupied by rebels and used as a safe centre for sea raids and piracy.
It was occupied again by the Ottomans and remained completely abandoned until recently, when restoration works were started by the Ministry of Culture. The fortress is built on a steep, flat rise, accessible only from the eastern side, where there is a spiral path. Its shape is oval and it is adapted to the morphology of the ground with alternate linear parts of wall and small bastions, to which stone-paved inclined floors lead. Because of the steep ground, the wall is interrupted on the north-eastern side.
In the area of the fortress there are two large, vaulted reservoirs that collect the rainwater from the stone-paved floors. From the remaining buildings, the church of the Annunciation and the gun-powder warehouse are preserved. The foundations of the barracks, the headquarters and other facilities can also be seen. The walls are built with local limestone, apart from the cordone, which consists of chiselled sandstone.