On the top of the hill you will find the ruins of an ancient fortified acropolis. The church is standing on the precipitous and almost inaccessible Eastern side. The acropolis was built in the Mycenaean period (13th cent. B.C.) , and it was inhabited until half of 12th cent B.C. During the 8th cent. new buildings were constructed, the fortification wall was repaired and eight small solid square bastions were constructed. The geometric town of Kastro was also built during this period and in the same area we find, much later, the city of Sifnos. The three sides of a double wall, surrounding the plateau still exists in a very good condition today, but the East side is almost destroyed.
Agios Andreas museum is the newest and most modern museum of the Sifnos island who opened to the public in 2010. The museum exhibits various finds selected from excavations of the area, as well as rich printed and electronic material about the Citadel of Agios Andreas and the rest of the island (Sifnos’ ancient city of Kastro, Sifnos mines, ancient towers) from the prehistoric times to the late antiquity.
The museum is open every day round the year (except from Mondays and holydays) from 8:30 in the morning to 15:00.