From the World Heritage inscription:
The Acropolis of Athens and its monuments are universal symbols of the classical spirit and civilization and form the greatest architectural and artistic complex bequeathed by Greek Antiquity to the world. In the second half of the fifth century bc, Athens, following the victory against the Persians and the establishment of democracy, took a leading position amongst the other city-states of the ancient world. In the age that followed, as thought and art flourished, an exceptional group of artists put into effect the ambitious plans of Athenian statesman Pericles and, under the inspired guidance of the sculptor Pheidias, transformed the rocky hill into a unique monument of thought and the arts. The most important monuments were built during that time: the Parthenon, built by Ictinus, the Erechtheon, the Propylaea, the monumental entrance to the Acropolis, designed by Mnesicles and the small temple Athena Nike.
I had an eight hour layover in Athens during my flight from Tel Aviv to Rome. I raced from the Airport with the one objective of visiting the Acropolis. The Acropolis is a small rocky hill in the center of Athens where the Parthanon and other temple buildings are located. There has been extensive restoration there during the 20th century. It is almost impossible to take a photo of any part of the ancient structures without having a modern bit of machinery or support in the photo. Despite the crowds, it turned out that two hours at the Acropolis was more than enough time to visit the site. You are restricted to only walking around the perimeter of the hill because of how old and fragile the ruins are. The Acropolis will also give you the best view of the city of Athens.