Kastro: The island's capital was located at Kastro from antiquity through 1836. The settlement was also the seat of the Archbishop of Sifnos from 1646 to 1797 and the Sifnomilos See from 1797 to 1852. Access to Kastro is through the old vaulted gates or loggias which were once protected by turrets. Kastro's streets and main square are built over the roofs of single-story dwellings, which are still used as warehouses. The homes chimneys were built perpendicular to the road and marked its path.
Kastro is still inhabited; there are a number of restaurants, pastry shops, and accommodations within its walls. Yialos or Seralia (from the Turkish serai or palace), the ancient port of Sifnos, is located at the southern foot of Kastro, where visitors can find accommodations and tavernas.
Churches - Monasteries: Several of the island's churches have been designated historic monuments because of their importance and architectural interest. Among them are the Panayia Angeloktisti at Katavati, the Monastery of Profitis Ilias Psilos, the Chrysostomou Monastery at Kato Petali, Panayia Gournia at Pano Petali, Ayios Antypas at Pano Petali, Ayios Konstantinos at Artemonas, Panayia tis Ammou and Panayia Konghi at Artemonas, Panayia Eleoussa at Kastro, the Panayia Poulati monastery, Panayia tou Vounou, and the Monastery of Panayia Chrysopiyi.
There are 227 churches on the island. Of special interest are the churches inside Kastro as well as the churches of Chrysopiyi, Panayia Vrysis, Moni Panayia Vounou, Angeloktisti Katavatis, Ayios Sozon, Panayia Konghi, Panayia Gournia, Panayia Ammos, Ayios Yioryis Afentis, Ayios Loukas, Ayios Konstantinos.
Ancient Fortifications - Old Mines: There are 55 ancient towers scattered around the island. The oldest date from the 6th century B.C. and the most recent were built in the 3rd century B.C., although only the Aspros Pyrgos survives in good condition. The towers were built after the Samians' raids and were used to relay messages to the ancient acropolises. Later the tower network was expanded to the entire island. According to Thucydides smoke and torches were used as signals.
Archaeological Museum: Exhibited at the archaeological museum in Kastro is a collection of Archaic and Hellenistic sculptures. The museum was renovated by the Culture Ministry in the early 1980s and has been fully restored since 1986.
Folklore and Popular Art Museum: Located on Iroon square in Apollonia, the folklore museum was established by the Sifnos Association to house a collection of artifacts linked to the island's traditions, from farming to household furnishings and local dress.
Museum of Ecclesiastic Art: The collection of ecclesiastic art is housed in the Moni Vrysianis and includes manuscripts, scrolls, and early editions, a Bible from 1796, relic cases, six-winged standards, chalices, icons, and an embroidered cloak.
Architecture: Settlements on Sifnos have a uniformity in their architecture. Kastro is laid out in a defensive pattern, easily discernible to visitors who wander its narrow lanes framed by marble reliefs and marked by vaulted passages or loggias that lead up towards the ruins of the central fortified section or castle. Most of the dwellings are two or three stories.
The island's traditional settlements are clustered in the interior, and over the years their boundaries have become blurred so that from some vantage points they seem to be part of a single, sprawling inhabited area. A paved walk runs from Artemonas, with its pretty mansions, through Ano Petali and Apollonia to Katavati, while another stone path links Artemonas to Ai Loukas, Exampela, Kato Petali, and Kastro.
The island's ceramics industry developed around coastal settlements which offer easy access to boats used to transport the wares.