Just got back a little over a week ago from a cruise out of Athens. We went to Athens a day early and found the metro very easy to use, even took it from the airport. In Limassol Cyprus we took the city bus, there was a stop right at the cruise port. On Santorini in Fira there were lots of places offering tours. We made the mistake of choosing Luxury Transportation Service (the driver didn't show up to pick us back up in Oia) but there were lots of other options that others on our ship had a good experience with. There was also a local bus we could have taken. In Europe, I use the same logic I do in the Caribbean, if there's something I absolutely want to see or port time is short I choose a shore excursion to make sure I don't miss the sight or the ship.