Kythnos, commonly called Thermia, is a Greek island and municipality in the Western Cyclades between Kea and Serifos. It is 56 nautical miles (104 km) from the Athenian harbor of Piraeus. The municipality Kythnos is 100.187 km2 (38.68 sq mi) in area and has a coastline of about 100 km (62 mi). Mount Kakovolo is island's highest peak (365m).