The correct answer to this open question is the following.
The Parthenon is the most iconic structure.
The Parthenon is an impressive temple located in Athens, Greece. It is a beautiful temple of white marble, that honored the goddess Athena, and was built at the top of a hill, Historians and archeologists believe that it was constructed approximately in 445 BC.
This impressive building was an important part of the so-called Acropolis, the social and religious center of ancient Athens. It is believed that Athenian Pericles was the one who ordered to built the greatest temple of the time to honor the goddess Athena.