A visit to the National Archeological Museum should be in your plans while you are in Athens. There are many beautiful and interesting exhibits like the "Young Horseman" or "Poseidon". There are also thematic exhibitions that are organized monthly. When you feel you 've seen enough visit the garden cafe in the museum under the shade of trees.
The National Museum of athen's contains findings from on the Acropolis, as well as around Athens and the major sites in Greece, including most notably the collection form Mycenae.
We visited the museum on the first morning of the School greece tip.
We only had a couple of hours in the museum, which was only enough time to look at the Mycenae collection and the stuff form the Acropolis. It's one of them where if you were staying in athen's for a full week, you would go to a few times because after the few hours we had i must admit it was starting to get a little boring.
One of the most interesting things about the museum is the completely bizzare statue's outside it. None of us were quite sure what they were meant to be...
We had lunch at one of the smalle cafe-bar's just outside the museum, it was delicious, but rather pricey (but what do you expect being in the middle of athens, right outside the museum?), and got rather engrossed in a debate with the teachers about the Elgin Marbles, taken from the top of the Parthenon, which currently reside in the British Museum in London.
This is a lovely respite from the hectic city. I've tried to find more out about the sculpture for information has eluded me ...