In Mid May we have 2 full days in Athens before a a 2 day Bus tour to Delphi & Meteora. Then a full day after the Bus tour in Athens before we depart to Santorini for a few days then off to Rome to stay with family. Any suggestions on how to fill these days we have in Athens? We would like to visit another island on a day trip from Athens one day if possible...
The most obvious, of course, is to visit the Acropolis. I would also recommend a visit to the Acropolis museum beforehand as it will help you understand the buildings there. You could accomplish both of these in half a day, and then spend the rest of the day wandering the Plaka, or walking up around the Acropolis. There are so many other things you could fill another day with. Watch the changing of the guards at Syntagma square and visit the nearby Benaki museum. Take the funicular up Lycabetus Hill for a great view of the city, or visit the ancient agora below the Acropolis. There is also the archaeological museum, which is a little further from the Acropolis, but is an amazing place also. You could easily fill two days and not be bored.
You could also take a day trip to Nafplio and Mycenae that can easily be combined with an olive oil and wine tasting. Nemea wine country is the biggest in Greece and on your way to Nafplio. There are a few agencies who offer this type of tours.