Former capital of the island until 1836, the historic village of Kastro is set on a an abrupt rock with a breathtaking view of the sea and built in such a way that the houses, connected by narrow passageways, form an impenetrable wall protecting the townspeople. It is an almost perfectly preserved medieval Cycladic town.
Site of one of the oldest settlements of Sifnos, there are still ruins of the 6th century BC, as well as columns and sarcophagi from the Roman period.
The small Archaelogical Museum houses a few interesting classical pieces.
From a pleasant path circumnavigating the village you can admire the picturesque little church of Seven Martyrs, perched on a rock that seems to rise from the sea, and a wonderful view of the Aegean.
Just outside the city walls there is an enchanting burial ground with the two churches of St. Stephen and St. John, which in the past were host to a major ecclesiastical school.
Kastro is also a cosmopolitan place, popular with tourists of different countries, attracted by its undeniable charm.