The Heart of Haiu

The Heart of Haiu is a myth about the most precious treasure that hides beneath the mountain of the same name. It doesn't only describe the inner most cave of said place, but the title also bears a second meaning. The Heart of Haiu is a nickname that was given to a consort of a long lost dynasty that is considered to be the first Inzu dynasty that ever ruled over nearby lands. This princess was the last representative of the mythical Haiu race of demigod origin that decided to stay with the humans instead of leaving like the rest of her people - for a very simple reason, she fell in love and losing her partner, the second Inzu king, was more painful to her than losing her original family.
She accompanied the king for many decades, but eventually her mortal life run short and when the king lost her, he hollowed up a series of tunnels into the Haiu mountain, which are considered the first man-made tunnels into this complex, and he also commissioned the best artisans to design a royal tomb for the former queen. He had the place filled with all of her favourite things and eventually, when his life run short too, he had himself buried next to her, so they can spend the eternity forever.
Many people have been incited to try and find the tomb of the former queen to enrich their lives, but no one has been successful, quite the contrary - many stepped into the mountain and never returned back to the surface. The other reason why anyone would want to risk something as dangerous as the fact that the queen is rumoured to have golden hair and many adventurers hope that they could get their hands on not just the money but godly powers of their ancestors.
Most scholars consider the person to be completely fabricated as the name of this royal consort was not even recorded in the history scrolls. However, most of them thing the heart of haiu is real, but instead of a person it is a precious gem that has been gifted to an important individual who has then been buried with it to be able to take it as an offering to the gods.