Zarim - World of Floating Islands:
A world that is only habitable at its highest mountaintops would seem a strange place to inhabit, but great landmasses above even those mountaintops provide the answer. Buoyed by Liftstone, vast tracks of land slowly drift in the ten mile band between the acidic Endosphere and the frigid and nearly airless Stratosphere, furnishing tens of millions of square miles of landform. Zarim is also littered with vast cloudbanks, and the collision of these clouds with landforms leads to deluges of rain and snow. To navigate such a world, flight is critical, and flight is common.
Even something as humble as a simple glider might be enough to navigate the ten miles of habitable atmosphere, as storm force winds blowing in open air simply propel upward (and of course, gliders can simply avoid such updrafts to descend); minor powers (Need to fill in) project their power through beamships, magical flying vessels that can blast with magical power.
The upper boundary of survivable space is marked by Jet Streams of remarkable power. These winds generally don't rip things apart (there's nothing necessarily mooring things against such winds) but they can become lethal hazards in terms of impacts. Specialized skips of the Jet Streams can allow for very rapid travel, but this is a dangerous trade. The Stratosphere itself has a large quantity of Liftstone, but it's also lacking oxygen and cold enough to freeze humanoids solid. At around 6 miles into the Stratosphere, blood simply boils from the low air pressure. It's possible to shelter against such conditions and various vaults, prisons and derelicts give some features to the Low Stratosphere, while the top of the Stratosphere (50 miles high) is a lethal void of space.
The Endosphere is a belt marked by the presence of oppressive heat, increased pressure, and a different chemical agent: Sulfur. Various Mercaptans reek and any ship trying to remain cool will be stained black from Sulfuric Acid. The foot of Zarim proper is hot enough to glow a dim brown-red. Heavy resistance to fire and acid is not sufficient, as the crushing pressure and overpressure of oxygen would kill. Though the foot of Zarim must hold the remains of every unfortunate failure to find land or those falling to their final destination, these conditions can destroy magical items, to say nothing of precious metals or other loot.
Zarim holds a lot of very unusual terrain and features:
Cloud Oceans. Water that descends too deep into Zarim is boiled and ascends upward, potentially forming features that slowly dance around the whole world for years. Though not truly static, gliding plants can add a green tinge, and birds generally find such patches to be feasting grounds. A Cloud Ocean has minimal ground of any kind, though humanoid foragers frequent such grounds.
Great Cataracts. The consequence of water rising onto floating islands is its eventual descent. Some Floating Continents are so large as to maintain a constant stream of water, water which can actually reach Zarim's foot and then immediately flash into steam. These features generally result in massive clouds flowing upward all around the Great Cataracts.
Liftstone Peaks. Zarim's liftstone supply stems from the world proper, but under conditions that can melt rock, Liftstone can accumulate and start to form an upside-down raindrop pattern as it slowly breaks free of the softened rock around it. Geological forces eventually cause the former peak to become a new island, although simply mining out the Liftstone can end the breaking.