In the early days of the world, there lived in the far north a tribe known as the Caldering. These were a fierce people, raiders by sea and land who lived between the call of battle and the great feasting halls of their Jarls, keeping to the oracles given out by the Völur. These seeresses who heard the voices of the gods guided the fates of that people.
Then the sickness came: an affliction that putrefied the bodies and minds of the people, put growths upon their organs and strange visions before their eyes. Hundreds failed and died, infants in their mothers’ arms and snow-haired elders all alike. With dread they watched the budding of the third eye upon the brow of loved ones, final sign of the disease they called the Rot. Unbeknownst to them, this taint manifested nothing other than their own inmost natures: the otherworldly force of the Void dwelt within them, and now quickened to bear fruit their mortal bodies, as they were, could not sustain.
A great lamenting arose from the Caldering, piercing walls between the realities. And so there came the day when the Völur spoke of a new call, proceeding not from the heavens but from the depth of the earth. They told the gathered people of an ancient being that had fled the ending of its own world. Of the curiosity that had drawn it to their own nascent world of Velmaneth. They told of a promise. It would save them, free them from this terror; it would make them whole, refine their being and open their inmost natures to mastery over the matter of reality, if they would but teach it of this world, joining with it in a compact of knowledge. It was then that the clan divided, those who chose to remain on the surface remaining the Caldering, and those who would in time become the first of the Underdwellers following the Völur to the lands beneath.
Led by the three Völur most sensitive to the call of the Ür-Mind, these last entered caverns that took them far from the sunlit world, descending, it seemed to them, far beneath the ocean floor. For days they travelled through the subterranean realms, passing fields of crystal and winding valleys of rotting stone, until, in time, they came to the edge of a lightless sea. From the stillness of the waters there emanated a strange sentience, and to it they felt themselves drawn. The three foremost among the Völur stepped into the waters, and knew this black ocean to be the manifestation of the Mind That Called. Their names were Sigfrid, Alfhild, and Inkeri, these sisters who would found the ruling bloodlines of the Underdwellers. There they first awakened to their natural psychomancy, their inner eye unveiled and bonded to the sight of the Ür-Mind by way of tithe, such that it would peer from within them for the remainder of their lives. Behind them, their people followed.
So by the Sunless Sea they dwelt, making it their holy place. They built themselves a city on its shores, its halls hewn from the living rock, gilded and adorned with fiery rubies lapped in sapphire and graven with the scenes of alien worldscapes. Sinnheim they called it, and for almost two centuries did not return to the realm above.
Aetheldred put down her quill, having finished amending that particular passage in the histories. The memories of the early days, of the Underdwellers’ birth from the Rot, had been all but expunged, so terrible had it been. But it had begun afresh. It demanded to be remembered. Her efforts had eventually saved her people from the effects of their own psychomancy grown wild, in spite of betrayal by one of the surfacers she had thought her ally, but the source of disruption remained to be removed. Whatever the White King had done, it would have to be dealt with. The tear in the Northern skies, opening onto the Void; something remaining from olden times that would need examination. And as to the one who had warned her, that early Underdweller and lone guardian who had once held back the Rot, she still required the help of her people. Aella...
Beyond the reaches of Sinnheim, a great stream of energy swirled, englobing the entirety of the Netherrealm. Soon it would be discovered to admit to the subterranean lands none but the Underdwellers themselves. For now, this would have to suffice.