Everfall is a city that is Autumn Eternal.
The city is built from the tree, and it draws materials from the world based on seeds.
Seeds are also the easiest way to open a portal back to the city, though other portals also exist.
It exists on an island surrounded by various strange biomes. Inland sea, and oddly hypersaline, thought to be the reason it is protected from strong magics.
No one has a background. Everyone is a blank slate, and need to train to explore the old world. There are natives to this world, but they are all elementally attuned to the biomes they live.