The Greek Islands are a fantastic place to travel, there's so much to go at and more to see every time you return. Santorini is the perfect gateway to The Cyclades (with regular ferries to various islands) and it's well worth spending a night or two here and seeing the amazing views and rugged landscape shaped by a 16th Century BC volcanic eruption.
Paros makes a great main destination with fantastic beaches, trekking (check out The Byzantine Way) & food. Eating seafood on Naoussa Old Harbour at night is an experience in itself!
If you've never been to the Greek Islands do some research online, find the places you'd like to visit and get planning. You won't regret it!