The archaeological site of the Olympeion comprises the temple of Olympian Zeus, Roman baths, Classical residences, a basilica of the fifth century AD, and part of the city's fortification wall. Hadrian's Arch is located just outside the site's fence.
The Olympeion extends northeast of the Acropolis, covering an area of fifteen acres between Vasilissis Olgas Avenue on the north, Amalias Avenue on the west, Athanassiou Diakou Street on the south, and the Tennis Club on the east. The Parilissia Sanctuaries are located south of the Olympeion along the banks of the Ilissos and Athanassiou Diakou Street, from the rock of the Olympian Land to the Kalirrhoe Fountain.
The temple of Olympian Zeus (124-132 AD), one of the site's most important monuments, had three rows of eight columns (tripteral octastyle) on the two narrow sides and two rows of twenty columns (dipteral eikosastyle) on the long sides. It once housed the chryselephantine (gold and ivory) statue of Zeus and the statue of the emperor. Sixteen of the temple's columns survive today, thirteen of them, on the east side, intact. Of the remaining three on the west side, one collapsed in 1852.
Other important monuments of the site are the Doric peripteral temple of Apollo Delphinios (500 BC), the Delphinion Court with its spacious courtyard and chambers to the north (500 BC), the gates of the Themistoclean Wall (479-478 BC), the temple of Panhellenic Zeus (131-132 AD), and the small peripteral temple of Kronos and Rea (150 BC). Other Parilissia Sanctuaries were located outside of the archaeological site of the Olympeion and the city walls. These include the temple of Artemis Agrotera above Ardittou Street (in modern Mets) and the temple of Pan near the church of Agia Fotini.