Netherhall, the City Below
Netherhall is a Sword and Sorcery themed campaign set in an underground city controlled by a group of cartels and guilds. Driven below centuries ago by religious purges, Netherhall eventually prospered, as the city above stagnated under self-imposed repression.
In this campaign, characters will be immersed in a world of official corruption, guild rivalry, political intrigue, and betrayal in a pressure-cooker of a city. As they gain renown among the thugs and street criminals in their neighborhood, they may rise in the ranks of a powerful cartel, but as always, betrayal and death are around every corner.
The Overview is a good place to start.