The Fall of Hvel-Runor

Below the Galentaur and beneath the Gnomish realm of the Neblinhala there lie the abandoned ruins of the ancient Dwarfish civilisation of Hvel-Runor.
Once it spanned many miles of natural and excavated underground caverns, from the Neblinhala all the way to the Sunless Sea, and encompassing what is now the Duergar city of Nidlhammer. Indeed, some say that the Dark Dwarfs are the ancestors of the once-proud Kingdom of Hvel-Runor, since corrupted by their thirst for gold and the influence of darker entities of the Deeps.
Hvel-Runor is thought to have thrived from the Age of Dragons, around five thousand years ago, to the end of the Arcane Wars about three thousand years ago, and persisted in some form until sixth or seventh century N.E. Its remains sprawl nearly a hundred miles from the Dragon Coast to close to the Elven Kingdom of Qualimor, with the Festering Marshes to the North and the Lake of Bones to the South, and dives many miles below the surface, too.
History has forgotten how Hvel-Runor fell. Some have it that the Dwarfs were enthralled by Mind Flayers and their civilisation stagnated as they transformed slowly into the depraved Duergar. Others maintain they were all but wiped out in a long and bloody war with the Drow. Still others believe their resources ran thin and the kingdom simply fragmented and scattered to the mountains.
Among the Dwarfs of the Ironcrag Cantons to the West there are some who still dream of recolonising their crumbling ancestral home. Their legends still recount the deeds and fables of Hvellic Dwarfish heroes of old, such as Duorik the Geomancer, Branag Firebeard, and King Uden the Patient.
Today much of Hvel-Runor is in various states of dilapidation. At surface levels there are still a few broken statues and paved tunnels that remain. Going deeper, it is thought that more and more of the disparate settlements that comprised the once glorious civilisation still remain relatively intact. Hvela’s grand halls stand, now silent and haunted. Nidlhammer, it is thought, is still occupied by Duergar under the twisted reign of King Moradin. Of Runor, the deep-lying capital by the Sunless Sea, nothing has been heard for centuries.