Once a girl looked into a piece of glass. What comes next is the interesting part. But what came before is necessary. Origin is always necessary. Even for a piece of glass.
This glass had been casually tossed aside at some point. Perhaps by a careless person. Perhaps by a purposeful one who knew what she had been about. It was a nice piece of glass. Wondrous. As though it had been made by lightening itself. Or, perhaps, it was just a perfectly timed break from a larger piece — that didn't matter, though; it still worked. But the girl didn't know that yet.
Before the looking came the wonder, as the girl marveled as to how some stranger could come to toss something so interesting aside. Something very much like magic.
But perhaps it wasn't tossed at all. Perhaps it had been left. Because suddenly the piece of glass was as magic as it looked, for in looking into it's icy depths, the girl disappeared into another world.
The glass was left then. Left as though casually left aside.
Perhaps all portals look that way. Or perhaps that is what happens with all lost glass.
I dare you to find out.