If you go to Greece, studying their ancient religious traditions, Elevsis (Elefsina), ca. 30 km outside Athens, is surely a place you ought to see.
Being one of the most famous sites of the ancient mystery cults, it has a history going back to ca 700 BCE. But to have a good understanding of the site, you need to know the story behind it, that is, the story of Demeter and Kore. You can read about the legend here: