I haven't strayed very far into creating my own worlds, actually partly because of the theology. I can't really improve on perfection.

So, in my "fantasy" stories set on earth I may have dragons or other creatures or alter the earth in different ways, but I try to make sure that it works according to Biblical standards. For instance, perhaps an ancient manuscript in one of my countries was found to be a translation of the Bible. No missionaries actually went there in real life (since the country is, dare I say, not real) , but the scripture is the same.
In Lensbearers of Huargia I've set things in a rather allegorical style, substituting spiritual spiritual truths for more tangible things. Still, though, the scriptures I reference are the same. "Your word is a lamp to my feet" in a figurative sense becomes a literal light in a dark or evil place, etc. I'm still working on how to flesh out the story world, but the goal is to present Bible truths in a new way, so that we can see them with the wonder we had at first.
My current Science-fiction Christmas musical is similar. The consensus, according to an article I read by Dr. Jason Lisle, is that (in theory) one could travel forward in time, but he would not be able to come back. He gave both scientific and Biblical support, but I do have time travel in both directions in my story. It's fiction, and I rationalize my use of it in a way that doesn't conflict with scripture. (At least according to my understanding)

And you have used polytheistic cultures as your inspiration, correct? Or rather modern fantasy stories that follow that model?