At the end of the Euripus is the so-called Serapeum, with a main hall covered by a grandiose ‘umbrella’ dome, surrounded by nymphaea and other rooms. The Serapeum was a spectacular summer triclinium, used for the emperor's official banquets, which took place in the evening, in the cool, with the flames of the torches reflected in the water basin in front.

The antiquarian excavations, made by Pirro Ligorio in the sixteenth century, by the Jesuits in the eighteenth century and by the French architect Louis Sortais in the nineteenth century, all focused on the Serapeum, which was the only visible structure. Egyptian sculptures in black marble were found, which today are in the Vatican Museums.

The Euripus basin remained completely unknown until years 1951-1955, when it was excavated by Salvatore Aurigemma. The excavation found four statues of Caryatids, (copies of the Athenian ones in the Erechtheion), and two statues of Silens along the west side, and other statues on the south side (Amazons, Rivers etc.). Thy are in the Antiquarium of the Villa, copies are displayed outside.

The monumental entrance of the Vestibule, preceded by the Paved Roadway, was reserved for the important guests who were received by Emperor Hadrian in this spectacular triclinium. From there the Euripus was reached, and after that the Serapeum. Its main hall has a semicircular shape and it is covered by an ‘umbrella’ dome: In the walls it has niches for the statues and others with stairs for the waterworks.
In the center there was a large triclinar crescent-shaped masonry bed (stibadium), on which the guests lay down.

The space in front of the stibadium had a small stage where actors, dancers and musicians entertained the guests with shows and concerts, songs, dances and music. The large dome worked as a sound box, the acoustics were perfect.

On the central axis of the Serapeum there is a long room similar to a grotto, covered by a barrel vault. Emperor Hadrian took his place there with the most important guests, in a dominant and protected position.
Its location was the same as that of the Royal box in our theaters: the spot with better acoustics, and also with the best view. In fact, from there a magnificent panorama of the Euripus was enjoyed, towards the over one hundred meter long basin of water that extended in front of the Canopus.

The Serapeum was completely reveted with precious marble, had mosaics on the vault and was enlivened by fountains and waterworks.
The Royal box where the emperor sat had a kind of bridge suspended over a basin of water, which cascaded down towards the stibadium, that was surrounded by semicircular canals where the water flowed, reaching the long lake of the Euripus,

Fountains and waterworks were fed by an aqueduct that was behind the building, equipped with two channels that took water from a large cistern excavated in the hill.