The temple of Zeus. One of the most abitious building projects. Just look at the huge size of the columns.
Started about 500 BC, left unfinished, robbed of some of its columns by the Romans, and finally 600 years after its start, at last finished by Emperor Hadrian.
View from the Acropolis
Hadrian's gate below, the massive temple of Zeus in the center, and in the upper left corner a glimpse of the Athens stadium.