There is a place, often referred to as The Faded Realm, which is nearly impossible for even the most powerful of planar magic to reach.
Ancient texts refer to the extra-dimensional labyrinth with an assortment of names. It is known in some references as the Labyrinth Beyond, and it has been frequently named The Faded Realm. Some texts call it The Sunder, while the most disturbing refers to it at The Forsaken Labyrinth. It is believed that this last name refers to the manner in which the Labyrinth seems to have been abandoned by its unknown creator, rather than suggesting that it has any ties to The Others.
It is known to have been considered the territory of a powerful Archmage in the time of the Vallahorienne, who is said to discovered it as a relic of a former age, and claimed it to use as a menagerie, as a sanctum, and as a prison for his enemies (whom he would often transform into terrible creatures before placing them into The Faded Realm).
Later, in the time of Octavia Lucius, The Sunder was accessed by a powerful mage now known colloquially as The Fallen King. This royal mage discovered that The Sunder had begun to slowly collapse, and had believed himself a mighty enough ritual caster to bind the Labyrinth and prevent it from collapsing by using something that has been called a ‘Ward Stone’ ritual.
The Fallen King’s reach, in this instance, far exceeded his grasp. He underestimated the immeasurable forces at work within The Sunder and was nearly destroyed by the ritual- his spirit becoming trapped until it was released nearly many years later by the adventurers of Falconguard.