The impressive Kyrenia Castle marks the entrance to Kyrenia's harbour. Throughout the ages and reigns, it defended the city against attacks from both land and sea, and was often heavily besieged. Founding on a presumably Byzantine structure, the castle was considerably amplified under the crusader noble John d'Ibelin in 1208-1211, and under the Venetians who enlarged it to its current-day dimensions in 1540.

Its walls encompasses dungeons, an archaeological museum, the small Byzantine church of St. George and the Shipwreck Museum, which exhibits one of the oldest ships worldwide: a Greek merchant vessel carrying millstones and wine amphorae, discovered by diver Andreas Kariolou off Kyrenias coast in 1965.