We have a good amount of material fleshing out the Greek myths, which treated various figures as deities.

Today, we look at them as "mythical gods," which is different from "religious gods."

My question is whether there were any large groups of people who actually practiced a religion under Greek Mythology.

I'm curious as to whether they studied them as more than gods, i.e. they didn't just believe that the gods existed, but they piously believed in them and prayed to and under them.