You can't go wrong. Athens, the Corinth Canal, Sparta, Corfu on the west [island], Delphi, the Monasteries of Meteora, Trikala, the islands: Crete, Rhodes, Mykonos, Santorini, ...
In Athens the Acropolis, the Plaka, the Roman temple ruins at the base of the Acropolis, many tiny churches inside and out, the National Garden and Zappeio Park, Lykavittos Hill, and Kifissias Park. Outside of the Plaka Athens is a very modern city with tiny churches squeezed in anywhere.
Bring much more film than you think that you will need.