I always wanted to do a kind of shanty-town fantasy. The setting completely restricted to a vast sunbaked hilly favela of tin-sheet apartments and mud and filthy electrical cables and the sewer outlets of the 'proper city'. And every day colossal wheeled iron juggernauts, carrying travellers to the 'proper city', just plough their way through the streets, tearing up houses and shunting entire facades to either side, remaking the layout of the town. (And obviously every time one of these breaks down, the inhabitants charge in and ransack the land-ship and spend years trying to sell branded goods to each other). The slum's been there for so long that creatures have evolved to survive in it; there's a predator that lurks in the mud of an alleyway and imitates the sound of a lost tourist or a narcotics-dealer's whistle, there are little chimp-like squawking creatures that seem to devolved from feral children in order to survive on the rooftops. And so the whole narrative plays out as a cross between a crime saga and a frontier tale, with the various slum-dweller families desperately living day-by-day through dogged entrepreneurship - which may just result in their being robbed or murdered by the various gangs or desperate, hallucinogenic-tea-addled llone criminals - or making quick cash by committing daring raids against the iron convoys that pass through (a short, brutal life).
A fantasy slum as a slum, essentially, rather than 'colourful backdrop for Thieves Guild leaders, beggars and bandits who just hang about in an alleyway waiting to get their come-uppance when they foolishly threaten Badass McHero.' City of Gods, if you like.