For many centuries the sanctuary of Apollo at Delphi was the religious and spiritual centre of the ancient Greek world. According to tradition, Delphi was the geographical centre of the world, the navel, the meeting point of two eagles dispatched by Zeus from the ends of the universe to find the centre of the world. The site dates back to the 14th century BC and there are stories about killing the first python, the cults of Apollo and Athena, oracles and prophesies. For better details ask the Google machine.
I stayed in the seaside town of Galaxidi, a charming settlement that was known as an island as there was no access from the mountains surrounding it.