Brimstone

"...There is a tale of foul portal leading to a dark realm of fire and lurking evil at every step, pain, suffering...
Aeons ago, fearless Iron dwarfs made their way in there in seek of the new ores and metals. Fighting back the horrors of this unpleasant realm they managed to achiev their goal, setting up an forge. A mighty forge never seen before, set right in the heart of the mountain of fire..."
- "You mean a volcano Uncle?"
"Yeap, now stop interrupting me or I will stop..."
- "Nooooo...!"
"ol'righty then... where I was... aaah the forge...
...It allowed them to melt metals in ways never possible before, anywhere else in the overworld. However, the invasion took it's price.
The fel monsters sensed the presence of new world being available to conquer and to be set aflame, preparing their invasion in the dark corners of this Brimstone place the Iron dwarfs had harsh time to keep them at bay.
But something more terrifying caused them having nerves on nails... Despite they never saw it, luckily for them. Nobody knows what else lurks behind the shadows of that unexplored horizons. Elder scrolls rumor about an even greater evil as those fiends swarming the portal... something that impales even their fallen soulless carcases with primordial fear... making the grounds tremble under it's feet..."
"... yeah yeah... ol'right, ol'right we know that one already Uncle Ironbeard, now tell us another tale... pleeeeaasee..."