The Byzantine castle stands on a low hill above the old town, offering good views over Kalamata and the Messinian Gulf. Most of what remains dates from the Frankish period (13th century), when the Villehardouin dynasty of the Principality of Achaea built it up as a major fortification. The Byzantines, Venetians, and Ottomans all held it at various points, and the walls bear traces of all of them.
The castle grounds are open to visitors and host summer cultural events, including performances during the Kalamata International Dance Festival. The interior is mostly ruined but the walls and towers are intact enough to walk around. From the top, you can see the full sweep of the Messinian Bay and, on clear days, the peaks of the Taygetos mountains looming behind the city.
A small Byzantine church — the Monastery of the Holy Apostles — sits at the base of the castle hill and is the site where Greek independence was proclaimed in Kalamata in March 1821.