Kythnos sits in the western Cyclades, the first island after Kea as you head south from Attica. It is a quiet, unshowy place, known in Greece for its thermal springs and simple stone villages, and much loved by Greek families in August. Syros, to the east, is the busy hub of the group: Ermoupoli, its port and capital, is a handsome neoclassical town that runs all year, with ferries fanning out to Tinos, Mykonos, Paros and Naxos. Linking the two lets you swap the calm of the west for the easy connections of the centre.
The direct crossing is the problem. Ferryhopper, the booking engine behind our search, describes Kythnos as directly connected with Syros on several of its route pages, but it had no Kythnos to Syros page in either direction when we checked on 24 September 2026, and we have no sampled timetable. That usually means a ship calls on only some days of some weeks. Older listings on our own site could not be matched to any dated timetable, so we do not repeat their times and prices.
So plan with a change of boat in mind. The simplest version goes through Piraeus: Kythnos has sailings to Piraeus all year, fastest on Seajets high-speed boats, and Piraeus has boats to Syros every day of the year. Another goes through Lavrio, south-east of Athens, where a Blue Star Ferries ship leaves for Syros on 2 to 3 days a week.
Search your date for a direct sailing first; if one turns up, it will almost certainly be the quickest option. If not, a day with a change still gets you to Ermoupoli by evening on most dates, and Syros makes a comfortable place to land, with hotels, restaurants and connections onward right by the harbour.
