Just once, I'd like to see one of these threads about a new and unique setting that doesn't immediately feature entries that say "but the world used to be a normal fantasy world" and/or "the people came from a normal world, because obviously they couldn't just be from here".
Humans might not be perfectly adapted to live on the side of a tower, but that doesn't mean they couldn't be from there anyway. We aren't perfectly adapted for living on ocean worlds either, but we don't waste time describing Earth-like fantasy worlds (like Toril/Oerth/Krynn/etc) by going on about what terrible disaster caused most of the surface to be covered with water.