Two days of organized guided sightseeing in Athens including Acropolis, The Temple of Poseidon in Cape Sounion, the Archeological Museum, the monastery church of Kessariani and Daphni, should be enough to get just an idea of the city and its history.
One more day to explore it on your own and to walk in Plaka, the oldest and most picturesque neighborhood with narrow streets and many taverns.
The next three days you can use Athens as a departure point to day-trips to Deplhi, Argolis and the island of Aegina.
It is an ideal city tour for friends, families, even schools who want to combine it with their study.
Duration: 8 days. If you prefer a short trip or a long weekend you could leave the day trips out and keep just the days in Athens.