or better yet an area where the ground is dark during the day with a sun in the sky and bright during the night with a moon in the sky.
A Discordant Realm or something like that.
The funny thing is, it would be accurate to real Equestria even. In the first arc of the official comics, Twilight pulled out a map where a spot with strange anomalies can be seen and that is called "Sight of the Battle of Discord" (or something similar, I don't remember exactly right now).
It does not get explained what happened there, but some discorded things are sure going on there, so it's not farfetched that there is a landmark in Equestria where Day and Night are reversed.