The Parthenon is the emblem of the city of Athens. It is very impressive when you arrive there, although you'll already have seen it a thousand times on the TV or on postcards you´ve been sent, but it´s not the same as being there in front of such a famous monument. It is registered as a world heritage by UNESCO, and it´s now being renovated. It´s a bit annoying because you can not enter inside the temple, it was damaged so much by people that they are now trying to preserve it as much as they can . I recommend you arrive early in the morning so that you can enter straight away. There is a pass available for all the ancient sites, which you can buy the day before, and arrive at 8 when it opens to avoid the tour groups.