If you want to explore classical heritage of Athens do not hesitate to see this site http://www.discovergreekculture.com/tours/by-theme/classical-heritage. Discover Greek Culture is a tour operator who offers 5 different tours like Greek Essentials, Visions of Ancient Delphi, Gods & Nature in Ancient Greece, A taste of Greece and Night Walk in Athens.
“Greek Essentials” is a full day tour (09:15-23:15)
“Visions of Ancient Delphi” are a full day tour (08:30-19:30)
“Gods & Nature in Ancient Greece” is a 4 days and 3 nights tour
“A taste of Greece” is a half day tour (09:15-15:15)
“Night Walk in Athens” is a half day tour (15:30-22:15 or 17:00-22:00)