Twilight is corrupted by exposure to dark magic, and Celestia traps her in an extra-dimensional space called 'The Light Prison.' The Seam is a tear in space that is the exit to the Light Prison, but is usually invisible because the only thing that exists there is light.

A short story I wrote in late 2012 to accompany this piece of art I made. Yes, I drew the cover art. You can find it on my dA page here -- im-not-sue. Also featured on EqD drawfriends 653, #41.

This inspired me a little, when coloring -- link
It would be appropriate listening music, I think.