First off, I drew this in commemoration of my 500th submission to this account
Now, I've mentioned this a few times before, but I'll go ahead and explain again, since I'm guessing many people missed this before.
Myth lives in a nexus dimension (a place between several other dimensions, that doesn't really touch any of them.) Her realm is broken up into three parts: the first is a desolate, charred, dead planet named "What Once Was," the second is a set of ruins, floating above the surface of the planet, where Myth actually lives, named "What Is," and the last is the swirling vortex of clouds (that cover almost all of the sky, except for the horizon which is eternally in a state of twilight) named "What Shall Be."
The main island in Myth's floating ruins is covered in trees, with a huge stone circle in it's center. Within this circle of stone are several large, colored crystals, which waterfalls fall upon from What Shall Be. It is through these waterfalls that Myth watches stories of ponies, and chronicles them.
Myth is an alicorn, not because she is "princess" of this realm, but because she is it's only caretaker. Also, she does have the power to change some things beyond the waterfalls, but never really tries to, as she prefers to watch how things will someday work out on their own.
Side note: I've got several other stories, but since they haven't been refined to the point that I can post them online, I chose to stick with the main figureheads of my current three projects.
characters and artwork featured here are mine