what are hyperboreans?

In Greek mythology, an unvisited people of fabled virtue and prosperity, living in the land ‘beyond the North Wind’; in Herodotos they worship Apollo and still send offerings to Delos. This could refer to a lost Greek colony in what is now Romania, or even to the Swedes at the end of the trans-European amber route.

Hyperboreans

The race of people who were assumed to live in a land of perpetual sunshine and abundance beyond the abode of Boreas (North Wind).

The Hyperboreans were said to have interacted with the Greeks until two of their messengers, Hyperokhe (Hyperoche) and Laodike (Laodice), failed to return from the sacred island of Delos after delivering tributes for the shrine of Apollon.

There were also two graves at Delos for two virgins, Opis and Arge, who came from Hyperboria before Hyperokhe and Laodike, who were accompanied by the gods (probably Apollon and Artemis) and were honored by the Delians in hymns and ceremonies which required young men and women, before their marriage, to cut their hair and place it on the graves of the two girls.

Histories, book 4, chapters 13, 32-36

Wiki has an article on them, do you have more information?

If you are into it you might want to check Nietzsche's short reference to them.

Thanks, i will look it up.