Kythnos (Greek: Κύθνος) is a Greek island and municipality in the Western Cyclades between Kea and Serifos. It is 56 nautical miles (104 km) from the harbor of Piraeus. Kythnos is 100 km² (39 sq mi) in area and has a coastline of about 100 km (62 mi). It has more than 70 beaches, many of which are still inaccessible by road.