Acropolis in Athens is so prominent as it is on a higher ground that it can be seen from various parts of the city. Built during 500-400 BC, it is THE primary attraction in Athens. The area is well covered by the Athens Metro. The complex is dedicated to Goddess Athena, the Goddess of Wisdom and War. Within this ancient Citadel, the most prominent building is the Parthenon, a former temple. When we visited Acropolis, a lot of restoration work was going on (as can be seen in some of the pictures). During peak times, Acropolis get very crowded. Also, the locals are pretty protective about this treasure. When my Daughter (without her parents noticing) picked up a rock from near the Parthenon as a souvenir, one of the staff immediately came over and politely requested her to put it back. I was impressed. I just wish such dedication could be repeated everywhere.
Also, the Acropolis Museum is a must visit to learn of the long history of this site.