Ferry to Delos. Booking is for both ferries, to Delos and back to Mykonos, and you can choose which times you will leave and come back. There were three trips a day when we went, first leaves Delos at 10AM and first comes back to Mykonos at 1:30PM. Ferry departures are every one and a half hours or so.

We booked just the transfer ticket and had our own tour book downloaded. There is a wait to buy entry tickets on the island once you arrive. Tour guide group probably got about a 10 minute head start on us. We started in the opposite direction recommended and didn’t have crowds to deal with and were able to enjoy the ruins without waiting for a large group to see things.

You get the boat ride from the Old Port to Delos and back. That is it. There is not much to it. The boat is comfortable and spacious. You can stay outside or inside. There is a bar with snacks and drinks. They only take cash though, so keep that in mind. When arriving at Delos you will have to purchase the ticket to visit. It is 8EUR. There will be a big line (all the people that came with you on the boat), so I suggest you purchase the tickets to visit the site online in advance. No food and drinks are provided on the island, so get yourself some water before leaving the boat. Delos is great. You can really walk through the remains of a civilization, the site is well marked, and there are plenty of ruins in reasonably good condition. If you have one day to spare when visiting Mykonos, do not miss it.