I've been in Greece just once, in a well planned trip that, in a week, took us to three of the most beautiful islands. staring and ending in Athens.
The chosen islands were Santorini (the most interesting), Mykonos and Samos.
The connections were made by plane, except from Santorini to Mykonos where we had to pick the ferry for a boring 9 hours trip, with a stop in Naxus.
Boat was also a detail in Samos, allowing us several hours in Turkey, to visit Ephesus from Kusadasi.
A great trip of two weeks, allowed, after some days in the beach in Cesme, the discovery of Cappadocia, with all its wonders.
We started in Izmir, to make a second visit to Ephesus and Selçuk, before proceeding to Pamukkale, Konia, with two days dedicated to the area of Nevsehir, from where I remember places as Goreme, Ushisar or Zelve,
In the way to Istanbul, a stop in the salt lake before staying in Ankara.
The two days to Istanbul were insufficient, but I returned there for a week.