The ferry from Sifnos to Milos is a key Cyclades connection. The crossing takes about 45 min on the fastest vessels, with tickets from €6.50. Sailings run all year, thinning out in winter, operated by Aegean Sea Lines, Blue Star Ferries, Fast Ferries and Seajets.
Most people take this crossing as the second or third leg of a western Cyclades loop. Sifnos is the island of pottery workshops, walking paths and serious tavernas; Milos is the island of volcanic coastline, coloured cliffs and boat trips to beaches you cannot reach by road. Pairing them makes sense because the sea gap is small and the two islands feel completely different once you step off the boat.
You leave from Kamares, the harbour village on the west coast of Sifnos, and arrive in Adamas, the working port of Milos on the inside of its huge natural bay. Adamas is where the island buses to Plaka and the other villages start, so it is a convenient place to land even if you are staying in Plaka, Pollonia or one of the quieter villages.
Before you book, decide what matters more: speed or price. The high-speed boats are quick but cost several times more than the cheapest conventional seat, and the slow ships only run on some days of the week. If you are bringing a car, check that your chosen sailing takes vehicles. In July and August the high-speed departures fill up, so reserve a few days ahead.