The Expanse
If you go sideways from, well, everything, then you go to a place where things start getting very, very strange. There's a lot of names for it, held by both those on Earth and the denizens of beyond, and not every one of them can be pronounced by a human being's vocal cords. Plenty of them aren't even a sound. But we call it the Expanse, which is a decent enough moniker. You see, it's expansive, as in it's potentially infinite (well, we say that. Really nobody know how big it is, and likely no-one ever really well. Effectively infinite then), and it's expansive, in that's there a lot of stuff in it.
Imagine, if you will, a realm of pure cosmic, magical energy. A flowing psychedelic kaleidoscope of light and color and sound and emotion, where one can walk between stars and planets suspended unimaginably close to you in a backdrop of ever-changing celestial power. In this place what one perceived as matter is merely one's brain attempting to give reason to the sheer wonder that it is being forced to interpret, thought and belief are far more important than physical force. This realm is what we see when we dream and what all our minds touch, even if we don't know it. It's the pathway to infinity, the gateway to the higher and lower realms. And it is inhabited by all manner of beings.
You have Gods (who, by the way, are not shaped by us. Where they came from, it's not really known. Maybe from the raw power of the Expanse itself) that are straight out of ancient mythology, living in magnificent shining cities that are placed in sub-realms created by immense magical power and incredibly advanced technology (Hephaestus has been around for thousands of years. You can be damn sure he is not just still making cosmic horse-shoes). You have the Fair Folk, or Shapeshifters, or Trickster spirits, or whatever you want to call them. They are one of the ones that take a big interest in mortals. The Gods used to, but I think we're a bit boring now we are less willing to sacrifice virgins to them. Who knows. You have those things that live in the deepest, most perilous realms, beings with millions of eyes and tentacles and eternal thoughts. You have demigods, immortals and wizards ruling their own personal little mini-kingdoms. You have the city of Celestia, where the Perfects have their little utopia. You have a lot of stuff, is what I am saying.
And it's where all magic comes from. You want to cast a spell, you do so by drawing on the power of the Expanse and bringing it into the physical world. Doing this is hard and takes a long time to learn, so generally people tend to make deals with things in the Expanse that can already cast spells and get them to do it for them. It's complicated, but it works. You can go to the Expanse, if you know how, and explore the ancient ruins of cosmic civilizations, battle demons and gods, learn ultimate power. And the things over there, they can come here as well.
