What if the Goddess of the Ashen Vale could turn an area of negative geomancy (Abyssal demesne) into a Manse by using Moliation and Pandemonium? Instead of using architecture and planting groves in occult patterns she performs ritual slaughters to channel the Essence of the site.
Perhaps caves were expanded by a race during the First Age or earlier though they left few or no traces of themselves except madness that still pervades the place.
The cave beneath the mountains was already a hellish and disturbing place due to it's confluence of negative geomancy. Perhaps connected in some way to the overthrow of the Primordials, the haven of an early cult worshipping one of the Deathlords, or perhaps the realm of a society driven insane by one of the newly slain Neverborn long ago in Creation's history, twisting their minds through the thin veil caused by the region's concentration of Abyssal Essence. Whatever madness overtook them it's former inhabitants have long since vanished. No remains littered the cave floor, the ancient tombs sealed in it's bowels were found empty and the place was devoid of ghosts, or any animal that might live in a cave. Until Ghost Walker arrived.
Perhaps the same madness that warped it's ancient dwellers to perform the acts shown on the reliefs still lingers, or maybe it's the influence of whatever mysterious and inexplicable disaster that overtook them. As one studies the series of reliefs they become increasingly laden with doom.
