As the unsuspecting visitor approaches this place just below Acropolis, he sees what seems to be just a large rock. It is Areios Pagos, the oldest high degree court for homicides in Athens. Here used to be, also, an altar dedicated to goddess Athena.
It is also the place where, according to the Bible, apostle Paul did his preaching in 54 A.D. In Greece, the Christian religion had to step, literally, upon the ancient religion in order to expand.
Many people like to sit on the rock and enjoy the sunset. Every major Athens landmark is visible from here and Acropolis is just behind your shoulder.
...and some more