The Grey

The Grey or 'Mirror World' is a world forged to be the opposite of our own. In The Grey, the landscape, political history and culture all seems the same, but is at times strangely converted to be a darker, more evil twin to this one. In The Grey everyone has a dark opposite of themselves, or light opposite if you are a villain. These Doppelgangers populate The Grey and seem to have all the appearance of sentience and cognition. 
The Grey is a place that the Order of Grey often comes to. Many of their powers revolve around accessing or manipulating The Grey for their own ends.