Milos sits in the south-west of the Cyclades and Mykonos in the middle, so this crossing cuts right across the island group. It is a popular link for travellers who want both of the big names in one trip: the volcanic coastline of Milos and the town life and beaches of Mykonos. The direct option is a high-speed Seajets boat, and it only runs in the main season.
Milos is a volcanic island shaped around one of the largest natural bays in the Mediterranean, known for its dramatic coastline and beaches such as the white rock of Sarakiniko. Days there are spent swimming and exploring the shore. Mykonos is a sharp change of pace, with the windmills above Chora, the lanes of Little Venice, beach clubs and some of the best-known nightlife in the Mediterranean. Many people end a trip on Mykonos simply because of its flight connections.
Timing is the thing to check before you book. In the middle of summer the Seajets boats make the trip in under three hours, but in the shoulder months at the start and end of the season Ferryhopper's data shows sailings taking around 5 hours, because the boat follows a longer routing. Same company, same two ports, very different day.
It is also a pricey ticket: €97.70 for one adult when we checked, with no car fare listed. If you are on a budget, or travelling outside March to November, it can make sense to go via Paros or Naxos, both of which have boats from Milos and many onward sailings to Mykonos.