The surface is ruled by the Empire, which controls everything with an iron fist.
All magic is restricted.
Fantastic creatures like dragons and giants are killed on sight. And all who don't fit in, the misfits, the rebels, those with incorrect opinions, are sent to Avernum, an enormous underground prison. There, they live out the rest of their lives in the cold and dark. There are currently two games in the series, each for Macintosh and Windows.