I have another sugestion: the planet earth 250 million years in the future.
Have a look at this:
Future +250
You can use it for a fantasy setting sci-fi or whatever you prefer. I just though that the idea of playing in the earth even if completely irrecognisible is quite cool.
As for myths, magic, etc. I would have magic/psionic that works due to evolutionary development and people explaining the world, magic, etc. with the religion/myths that they choose create. Meaning that the explanation that they give have nothing to do with reality.
I'll try to explain a bit more. Some people might have a thunder god, at the same time they have use of some thunder/weather magic or psionic hability. The teaching of hability is associated to the religion but that doen's mean that the god is real. Religions become a way you can study those habilities.
You can have chaos as a consecuence of mutations as a danger.
You can have very weird creatures.
You can have various intelligent species coming from different evolutionary branches, i.e. lizardmen, plant like elves if you want, various human like species coming from the homo sapiens and even ducks!!!
I think that's all.