I just finished reading Boneshaker, a steampunk-zombie-dungeoncrawling novel by Cherie Priest. And now I keep thinking about Boneshaker as a setting for Torchbearer.
Like towns could be in the Outskirts or some of underground refuges Inside the Wall. The rest of the Walled City is clearly a wilderness of serious dangers, running two blocks on the street is crazy risky. But there’s plenty money to be made, if you’re desperate enough to risk the fog and rotters; either infiltrating the underground compounds of other factions or finding lost loot and secrets amongst the crumbling ruins of the city above.
I imagine it wouldn’t be hard to just colour in the steampunk—the gas-masks and “magic-like” tech—as magic spells, divine favour, alchemist or apothecary tricks. But I think it also wouldn’t be hard to port the walled city, the poisonous fog, etc., to the fantasy world of Torchbearer. I mean, there’s clearly at least one mighty wizard and his tower in the novel.