The Leonidaion, situated at the south-west corner of the sanctuary, outside the sacred precinct of the Altis, was a large and luxurious hostel for distinguished visitors to the Olympic Games. It was built in approximately 330 BC and was remodeled twice in Roman times. A dedicatory inscription partially preserved on the epistyle of the outer Ionic stoa records that the building was erected by Leonidas son of Leotas from Naxos, who was both architect and benefactor. His statue stood at the north east corner of the building where its inscribed pedestal was found.

This large, almost square building consisted of a central court surrounded by a forty-four columned Doric peristyle, off which rooms opened on all four sides. The west side was wider (fifteen metres) than the others (ten metres) and housed the largest rooms. Outside the building ran a continuous colonnade of one hundred and thirty-eight Ionic columns. In Roman times, when the building became a residence for high officials, an elaborate pool was laid out in the middle of the court.

The monument was uncovered during the recent German excavations and its surviving wall-plaster was recently restored. Fragments of the building's elaborate terracotta gutter are on display in the Olympia Archaeological Museum.