Legends speak of the world before this one, where people lived in a humongous cavern, with an infinite tunnel onto near-nothingness occupying half of their view at all times. Somehow, these people were stuck to one wall of this cavern, and never in danger of drifting into that endless, sparkling abyss. But it was a fragile, impermanent world, and a fickle god destroyed it all, releasing the people from the force restraining them and filling the abyss with fire. Only those who had predicted this day and built this new world in preparation survived the destruction of the old world.
By grinding down bones to produce a form of dirt and providing artificial suns, the ancients managed to eke out a sustainable existence in large caverns. Their descendants, the agriculturalists, have since expanded and improved on that practice.
There are those who prey upon the agriculturalists, especially among the creatures that live on souls or calories.
Some have portals to the ruined remnants of the old world, which they venture out into in order to collect large hunks of unrefined ore. Few creatures who need to breathe find success in the mining industry.