Located on the west part of Kastelorizo, Palaiokastro is the oldest and most important monument on the island. It is an ancient citadel, built on the site of a Dorian Acropolis of the 3rd century BC. It stands on the island's second highest mountain (252 m) and was in use until the period of the Italian occupation.
The castle hosts various structures, including houses, churches and cisterns. Only two of the churches are still preserved in good condition, the church of Agios Stefanos built in 1850 and the church of Panagia (The Virgin). The church of Panagia has a beautiful pebbled courtyard that dates back to 1858 and remarkable icons, dating to 1852. The churches of Agios Nikolaos, Agia Lesa and Panormitis were destroyed during World War II. The houses are all in ruins and abandoned. Remarkable are the partly impressive large cisterns of the castle carved out of the limestone rock. In addition to cisterns, towers and parts of the Hellenistic defensive wall have also been preserved.
The Order of the Knights of St. John did not significantly expand the ancient fortifications. On the other hand, the Italians used the castle as a fortification site, installing anti-aircraft guns and air raid shelters during World War II.