Found a glitch in one of the Ancient Magic Hotspots.
From my memory (UPDATE: Its the hotspot right outside of Keenbridge) it was in the central-eastern part of the map. So in the Hotspot there is a tower that you can broom up to and slip by a small gap in the ceiling.
You find yourself in the upper part of the tower, nothing of interest up there...until you fly up towards the ceiling of the tower. Once you hit a certain height, you'll glitch into a blue hell, where the only things you can see are buildings and landmarks off into the distance. I didn't get to explore in it, but if you fly down, you'll be back in the tower. Very reminiscent of the San Andreas "using the jetpack in Ganton gym" glitch.
EDIT: you cannot explore the blue hell, you only hit an invisible wall and eventually end up back at the tower.
Once up in the tower, though, you're trapped, you can't go back down through the gap you came in from. You'll have to fast travel elsewhere to escape the tower. (UPDATE: it is possible to escape, you have to fly around the blue hell until you hit a hole in the tower where you can escape from, once you do, you'll start moving, then the blue hell disappears and you're outside the tower.)
I'll do more research on it, unless I'm late and gay, but I don't remember seeing anything posted about it and thought it was interesting.