Welcome to the Darkness. Welcome to Cavernia.
Before the Catastrophe, the world had many names. Dwarves called it "Tanukta" and the Elves call it "Yenmara". But such names, like the world they once knew are gone forever. The new world is below ground and is commonly referred to as Cavernia.
Two thousand years ago, an epically powerful group spell that had the best intentions went awry and unleashed a massive amount of arcane energy that turned the surface of the world into fields of deep ash and scorched and desolate wasteland. The very sky itself burns with constant firestorms and explosions. Acidic rains fall, rivers of mud flow and lakes of poisonous water stagnate.
Cursed ash, a by-product of the arcane cataclysm, constantly falls upon the land. The ground is covered in it. Lakes and rivers are choked with it.
Beneath this desolate, wasted surface the real Cavernia begins.