I will be traveling to Athens for a cruise in Sept 2015. I would like to see the sites in Athens as well as go to Santorni. My flight arrives a Saturday but the cruise does no t leave till wednesday. I would like to know is it possible to take a ferry to Santorini for the day or do i have to stay over night? Or maybe whats the best possible way to see most of the islands? I have read about taking the bus to athens from Piraeus but was wondering on others opinion on making the most of the 4 days precruise.