Kea, also called Tzia, and Kythnos are the two Cycladic islands closest to Athens, neighbours in the western chain that most visitors reach from the port of Lavrio. Both are favourites of Athenians who come for long weekends, and both stay refreshingly low-key compared with the islands further south. Linking them by sea turns two short breaks into one easy island-hopping trip.
The islands have different characters. Kea is hilly and green by Cycladic standards, with its hilltop capital Ioulida and a web of old footpaths. Kythnos is drier and quieter, known for the thermal springs at Loutra and a long coastline of coves and beaches. Going from Kea to Kythnos is a natural next step south if you are working your way down the western islands.
The catch is frequency. This is not a busy corridor: Ferryhopper lists sailings on only two or three days a week, and in last year's data it was Blue Star Ferries that ran almost all of them, with Karystia Travel appearing once a week in a single month. That means your dates may have to fit the boat rather than the other way round, and it is worth booking once your plans are fixed.
The good news is the price and the pace. The crossing takes between 50 minutes and about an hour and a half, and a seat was listed from €6.50, a modest fare for any Greek ferry. If the direct boat does not run on your day, you can always go back to Lavrio from Kea and take one of the more frequent boats from there to Kythnos.
