Here’s a set of suggestions for how to implement some of the touchstones we listed like “floating islands” and “steampunk trains”.
The world is criss-crossed with lines of energy (ley lines, ether, quintessence, call it what you will). At higher elevations, away from the heart of the world, the flow is weaker, while in the lowest possible valleys, it grows dangerously intense.
Geography is such that multiple “tiers” or “layers” of land exist, sometimes supported by solid stone, other times levitating in the air. The supporting stone by itself isn’t strong enough - ley lines connect the lower and higher tiers and form an unbreakable pillar.
Some scholars believe that some great upheaval in the past caused this unusual disturbance. Others think that parts of the world were deliberately raised up by ancient cultures and potent magic, perhaps to create an impenetrable boundary from less-gifted rivals.
Invisible lines of energy still connect the lower lands with the higher ones, or bridge the gap between the “surface” and the occasional floating landmass. Magitek has allowed inventors to create “mist barges” that ride these ley lines, like a gondola lift or a train on invisible aerial rails. Mist barges cannot deviate from their paths, making them unsuitable for general transportation, but excellent for moving people and cargo from one landmass to another.
At the lowest elevations, in deep valleys or rifts in the earth, the accumulated magical power does strange things to nature. Animals, plants, and even the occasional humanoid have been spotted, growing to giant size, or gaining strange powers.
Stories of millennium-old animal gods, giants, chimerical horrors, and familiar phantasms stem from encounters with these beings.