Τhe Venetian Quirini Fortress with the heraldic shield of the family. In architectural terms it belongs to the fortified settlement category where the outer walls of the houses are the curtain walls with small openings as murder holes. The home of the Quirini is built around the entrance on the eastern side and covers two storeys. Until 1956 the entire fortress was inhabited. Inside the fortress are two churches painted white with ornate bell towers. At the entrance is Panaghia Kastriani (Evangelistria) and at the end Aghios Georgios. The Panaghia Church was built in 1853 above the arched entrance to the fortress. Inside there is a founder’s inscription dated 1413 and the heraldic shields of the Quirini. Aghios Georgios was built in 1790.

The Castle of Agios Ioannis in the southwest coast of Astypalaia dates back to the Byzantine times. The construction of the castle coincides with the period of time when piracy was flourishing in the Aegean Sea. The construction of fortresses in locations that were far from the sea or up on hills, was a common measure of protection of the population from the raids of pirates and other enemies. The location of the castle of Agios Ioannis can confirm the aforementioned theory. It was built on the highest spot of the island, above the large homonymous beach which is only accessible by boat or on foot by following the mountain route.