The oracle of Delphi is a location in Greece in the South West corner of Mount Parnassus. The Greeks called this the the belly button of the world. Part of the reason for this was because the most important oracle in Greece was there. People from all over Greece would travel there to gain insights from the god through the priests, who served the temple of Apollo. For this reason, it was considered a panhellenitc sanctuary. It was also the place of the Pythian games, which were held every four years.
Delphi also had a few central maxims of Greek culture, such as "know thyself," "nothing in excess," and "make a pledge and mischief is near." In short, it was the place of wisdom and knowledge.
Delphi also plays an important role in literature. As many people go to seek the wisdom of Apollo. We even see this in the time or Romans, who sought the wisdom of Apollo.