This is a hallowed burial site marked by the mythic menhirs (stone circles) of Unknown, reputedly constructed in ancient times by the Yuir of Unknown and used to travel over long distances.
Recently it was taken by Unknown and made into a summoning circle for the horrific Gorthok the Thunderboar, a minion of the god of storms and destruction: Talos.
Long ago the heart-turned-emerald of the buried warrior-priest (or wizard-king) was stolen from the tomb and only recently returned to the site by Unknown, having retaken it from a Unknown within Unknown.
(See: wiki)