Alternately, this could be called Nethwenta 101. This will be the first in a series of 101s about the ancient empires of The Known World, hopefully.
The empire of the Glenwighta race was wide and its tunnels extended far beyond the modern day borders of The Fell Peaks/Kusseth. Long before Kaleshmar fell, the Dwenoren and Glenwighta frequently met in border skirmishes that filled the dark places of the world with cries of pain and the scent of blood. The Dwenoren were still fierce warriors then and had an edge over the Glenwighta, they had no need of light. The Glenwighta however, could always smell the Dwen coming. It was a brutal war that the Glenwighta have no knowledge of any more, and the Dwen only dimly recall the valor of those days.
In those days, the Glenwighta had almost no knowledge of sorcery, and perhaps this is the reason they had no knowledge of their innate weakness to it. It was considered too volatile a force to play with. If even one spell misfired in a violent detonation of arcane forces, it could bring ruin to all nearby maze-cities as the tunnels of Nethwenta channeled destructive energies from one city to another down smooth halls of carved stone. Or worse yet, if one city collapsed into a ruin of rubble, it could disconnect others from the food and water they could not harvest from their own areas.
The Glenwighta of Nethwenta were a highly industrialized society, but their industrialization was a long, slow process that was heavily monitored and only grew when the Sol and Okwighta agreed that it was time for a revolution. This process of technological advancement put them decades behind the Dwenoren and Greyskin Abraxens, but it allowed for a very stable growth and development. A more modern example of this, some clans of Okwighta were experimenting with early firearms even before Kaleshmar fell, but the technology was too dangerous and prone to unreliability, so research continued. Meanwhile, when the Dwenoren "invented" firearms and distributed the technology to other races, millions lost life or limb when poorly combined chemicals or improperly machined gun parts caused catastrophic failures to the weapons.
There were of course elements of Nethwenta society that demanded progress at the expense of safety, believing that through industry and learning they could overpower any foe that came against them. They were a small fragment of the society and their goals were not welcomed. They were practically outcasts, and often congregated in small enclaves of like minded individuals. When Nethwenta grew too populated for these secretive little enclaves to exists at the outskirts of its borders, these almost-outcasts left the earth and journeyed away from their people into the world above. Their absence was a footnote in the now nonexistent history of the Glenwighta, and they were not missed.
In that time, the Solwighta were regal kings clad in plate armor of dark metals and were waited upon by their warrior cousins the Conwighta. The kings of Nethwenta were noble rulers, long lived and mighty from long years of battle. The tunnels the Glenwighta lived in had once been full of fell creatures, the Solwighta and Conwighta prosecuted a long and bloody campaign against these creatures while the Okwighta remained safe within the early borders of the kingdom creating a series of interconnected settlements for their cousins to return to when they grew too weary of war. It was this ancient initial conflict that prepared the Glenwighta for when they would eventually clash against the ancient race of Dwenoren.
The empire of Nethwenta in its hey day was a peaceful kingdom and almost an underground utopia. It fell because the Nagsulen (now called Fell Humans) were tricksy and the Solwighta were unwilling to exterminate a race merely because they were mutants warped by sorcery. Unfortunately, this led to the enslavement of the Glenwighta people and the complete destruction of their culture.
Perhaps somewhere deep beneath The Fell Peaks and Kusseth there are some remains of the Glenwighta tunnels and maze cities, but they would likely be infested by the bizarre creatures that the Solwighta once waged war upon. Such ruins would be rich with strange devices and weapons and armor forged of curious materials unlike that found in the surface world.