Syros and Kythnos sit on either side of a line that splits the Cyclades in two. Syros is the hub of the central islands, and Ermoupoli, its port and capital, is a stately neoclassical town with boats heading in every direction. Kythnos belongs to the quieter western chain: an island of thermal springs at Loutra, simple stone villages such as Chora and Dryopida, and harbour tavernas at Merichas, far better known to Greek families than to foreign visitors. Swapping one for the other is a lovely change of pace.
The direct link is the weak spot. Ferryhopper, the booking engine behind our search, describes Kythnos as directly connected with Syros, yet it had no Syros to Kythnos route page in either direction when we checked on 24 September 2026, and we have no sampled timetable. That usually means a ship calls at both islands on only some days of some weeks. Older listings on our own site gave a time, a fare and two operators that we could not match to any dated timetable, so we no longer quote them.
The trip that always works goes through Piraeus. Boats leave Syros for Piraeus every day of the year, and Piraeus has sailings to Kythnos all year, on anything from one to seven days a week, with Seajets high-speed boats and the conventional ships of Aegean Sea Lines and Fast Ferries. You change boats without leaving the port, though Piraeus is big, so allow time to find your departure quay. On the days when Blue Star Ferries sails from Syros to Lavrio, the port south-east of Athens that serves the western islands, you can connect there instead.
Start by checking which days a boat leaves Piraeus for Kythnos in your travel week, since that is the leg with the fewest sailings, then book a Syros departure that gets you to Piraeus with time to spare. Search the direct route too: if a ship calls at both islands on your date, it will be the simplest option.
