Floating islands are a staple of fantasy fiction. It’s easy to see why: floating islands are cool. Take an island and push it into the sky and it goes from mundane to extraordinary in moments. It is a shame then that most sky islands are kind of boring. It is strange that the underground (a thing th
This assumes anything would evolve in such an inhospitable environment. If it’s cold and oxygen is thin, it’d likely be as barren as mountain tops.
I’d suspect they would perhaps be a popular place for large flying creatures who might like to make nests there in safety and use them as resting locations during long migrations
They’d probably also attract humans and their ilk who wish to capitalize on the islands’ natural defenses as well. Though this would obviously come at a cost of seclusion. Goods would be difficult to transport and would probably cost more than in a city on the surface.
I’d imagine they might still find settling up there worthwhile to mine whatever unique materials these islands hold. Perhaps the islands are composed of rare magical minerals that cause them to float. Minerals that would probably fetch a high price.
And as the minerals are depleted, the island begins to sink until it has been completely depleted and it settles on the surface, crushing whatever lies below.
If the citizens care enough to ensure it lands in a usable state, and the city has developed a diverse enough economy, it may survive and go on operating as a regular city.
Most would probably be abandoned once depleted, leaving behind large mineshafts and abandoned buildings for nature or squatters to reclaim, which could make for fun dungeons.
There’s no rule that a sky island has to be above the tree line. Even a modestly tall mountain’s height would put it far out of reach from any society without materials or a design for a hot air balloon. After all, you cannot simply hike up to it.