No matter where you go, any visit to Greece is better than none, but Its a real shame that so much tourism is devoted only to the Greek Islands.
The Greek mainland has great beaches too and many, many, many more ancient and historical sights to see. Top ancient Sights-Sites
Its also cheaper in many cases than hot spot islands like Mykonos, Santorini, Rhodes, Cos, Corfu and Crete, which, while highly recommended in their own right, hardly convey the whole story about Greece and its incredibly varied landscape and history.
High season why wait in line for service on these popular islands when you can rule the roost and be treated like a king for less in many slightly off the trail mainland locations?
Organized Tours only go to the so called major sites and dont go to all the ancient sights/sites (even those pictured) so you need to rent a car if you really want to explore ancient Greece. Still some sites have a lot more to see than others as this photo demonstrates.