The Lair of the Sphinx, also called Ruined Temple and strange ruins, was the ruins of an Isu site located on the southern shore of Lake Kopais in Boeotia, Greece which housed the Sphinx, a hybrid creature result of the Isu's Olympos Project.
Within the ruins was a statue of a Sphinx standing on a pedestal, and around it were pillars with various pictographs. By night, the pillars lit up, and seemed to flare with unearthly fire.
During the Peloponnesian War, the site was visited Gorgias, a Boeotian historian and an ally of Pythagoras. He met there the Spartan misthios Kassandra, who had been sent by Pythagoras to retrieve an artifact needed to seal Atlantis. While Kassandra was looking for the other half of the medallion apparently required to summon the Sphinx, the creature slew Gorgias. When Kassandra returned, she defeated the Sphinx by answering her riddles correctly. Kassandra then claimed the artifact masquerading as one of the Sphinx's feathers.