Need to make a last minute fantasy city/town?
I got just the trick for you. Exaggerate a city you’re already familiar with. A hometown? Capital? Friend’s town? Exaggerate it with fantastical elements and maybe even inside jokes. Not too long needs to pass before you got a convincing fantasy city.
A small rural town known for its flowers? A secluded village swallowed by giant boughs of wildflowers, where masterful but painstakingly traditional druids live.
A city with terrible potholes and construction that never ends? Make it a city built upon massive caverns and canyons, repairing the results of constant dangerous dragon attacks.
Detroit? A city of thieves, that upon entering, with each passing hour you yourself become more and more thief-like.
Really do this! Exaggerate more than one element, and you get a place even more unlike with what you started from.