Kimolos is often the last quiet stop of a western Cyclades trip, a short hop from Milos but a world away in pace. When it is time to head back to Athens, you do not have to go through Milos: direct ferries run from Psathi, the little port of Kimolos, all the way to Piraeus.
You have two kinds of boat to choose from. Conventional ferries from Fast Ferries and Aegean Sea Lines sail all year and take about 6 hours, stopping at other islands on the way. From June to September, Seajets adds a high-speed boat that reaches Piraeus in 3 hr 25 min to 3 hr 30 min, which roughly halves the journey.
The price gap is large. When we checked, the conventional ships started at €42 to €43.50 in Ferryhopper's monthly data and the lowest single fare shown on the route was €39, while the Seajets boat started at €78.70. For a family with a car, the slow ferry is the obvious pick; for a couple racing to a flight, the summer fast boat can be worth the premium.
Service is not daily outside summer, and even in season each operator sails on selected days only. Pick your departure day first, especially if you have a flight to catch from Athens, and leave yourself a night in the city before an international flight. If nothing direct suits, crossing to Milos opens up many more sailings to Piraeus.