Exosta

"Legends tell of a time, many thousands of years ago, when the world of Exosta was full of life. Humans, Orcs and Ratmen - some claim even a few Goblins – lived on the surface, in the open, under a clear blue, and often lightly clouded, sky. No-one really knows what caused the sun to stop shining, but as quickly as the sun died, so did this golden age come to an abrupt end."

- Arx Fatalis Manual

Exosta is the world setting of Arx Fatalis, where the sapient human, goblin, troll, and ratmen races lived until its sun ceased shining, driving them underground.