The capital of Greece is a huge modern city, but one with old roots and many many monuments dating back to the dawn of civilization.
The main monument to visit is of course the Acropolis, the hill upon which the Parthenon and other important sites are located. The climb can be hot, but it is worth your while.
The Plaka is one of the nicest areas of town: ideal for shopping and wandering through cobblestone streets or sitting down in one of the many tavernas.
Athens is a good base for exploring the region: Epidaurus, Corinth and Mycenae can all be see on a trip from the capital, Cape Sounion, Delphi and Marathon (42 km away) are also good options.
Pireaus is the port of Athens. It is a very dirty place but also the place to start your trip to the greek islands.
Athens hosted the 2004 Olympics.