Drakonheím: City of Bones

From the introduction:

Drakonheim is a fantasy city full of intrigue and surrounded by dangers. Goblins dwell in the sewers, undead walk the streets, and aristocrats scheme for greater power. Hobgoblins ride across the northern plains, lizardfolk rule the southern swamps, and all manner of monsters hunt in the western mountains.

Drakonheim is a system-free setting; you can use it with any fantasy roleplaying game. It can serve as a quick stopping point, or as the center of an entire campaign.