Delphi, Greece: Once regarded as the omphalos or the “navel” of the earth - Delphi was the temple of the Olympian deity Apollo, the son of Zeus, during the Classical Greek period. This temple, on the slopes of Mount Parnassus, was where people would come to have their future foretold by the Oracle or one of his priestesses. Not all of their prophecies were correct; in fact, the priestesses were mostly tripping on ethylene gas.
"…inhalation of even a small amount of ethylene can cause both benign trances and euphoric frenzied states… where the subject could sit up, hear questions and answer them logically, although the tone of their voice might be altered, their speech pattern could be changed, and they may have lost some awareness of their hands and feet, (with some it was possible to have poked a pin or pricked them with a knife and they would not feel it). When patients were removed from the area where the gas accumulated they had no recollection of what had happened, or what they had said… According to Plutarch, who witnessed many prophecies, all of these symptoms match the experience of the Pythia in action.”
- extract taken from Wikipedia
You gotta love Greek gods and goddesses!