There are some good resources available through the Google to find related information to flying in Santorini, Greece.
An article from JCB Visuals:
Flying Your Drone In Santorini | JCB VIsuals
Some Regulations:
http://www.ypa.gr/userfiles/fa3cb89c-ac1a-4d4b-99ab-a34f011804e1/HCAA-UAS-Regulation-Final.pdf
Spark Pilots:
Can I fly in Greece?
Mavic Pilots:
Greece drone laws
Hellenic Civil Aviation Authority:
https://dagr.hcaa.gr/
From what I gleaned, generally, drone use is accepted and nobody really minds it so long as you are flying safely and sensibly. They do have laws and regulations in place, but they generally aren't enforced. Overall, it looks like the 'good guy' thing to do is follow their laws and comply with their regulations or just not be an idiot.
Have a great vacation!