I initially assumed my world was going to be pure fantasy, but the more I think about it, the more I consider having the story take place somewhere on Earth, either as alternate history or the far future. I have some requirements for the broad area around the main character's home due to events in the plot I've already written:
The main area where civilization tends to prosper is a temperate zone, not unlike most of North America, Europe, East Asia, etc.
Next to the MC's rural hometown is the Poison Land, a cold volcanic desert, ideally on the leeward side of a mountain range, that produces obsidian and basalt. It has moderately toxic soil to the extent that the people there have an inborn resistance to it and can in fact be quite healthy and strong, but many are noticeably diseased and/or deformed. Beyond the Poison Land should be more land, not necessarily poisonous but probably wild.
In a different direction from the Poison Land is an ocean, ideally warm, that experiences infamously intense Summer Storms, but has a good amount of habitable islands with some of the more advanced (medieval to early modern tech) societies. One of these islands is the capital of a major kingdom whose influence extends to the mainland and has a natural fountain with inexhaustible drinkable water. (the Fountain is important to the plot)
To the north - and it really should be the NORTH for cool factor, although I'd also consider a warmer Antarctica - is an isle or continent known for its giant people and cold weather, who have domestic bison and either loads of farmland or even more loads of wilderness to hunt from.
Somewhere nearby the 'hub' realms is a forest of giant trees, like the Giant Sequoia, where the majority of this world's proxy-wood-elves live. Bonus points if it's adjacent to or in a jungle, and adjacent to or on the Isle of Giants, and in a week or so's riding distance from MC's hometown.
I'm also considering higher oxygen levels and more air density so we can have giant bugs and giant flying animals, but that's not a hard requirement.
What I need to know is: Does a region like this already exist on Earth today? And if it doesn't, then could it exist as a result of climate change over the next million years or so? Because if not, that means I'll have to set the world on a different planet, which radically changes the course of my worldbuilding style.