Situated on the most remote part of the world, a citadel was constructed millennia ago on the South Pole. This is not one of those high end resorts for people with nothing better to do with their money. It is a haven for the ascended beings known as Shades. The energy based lifeforms do not require a core body temperature in order to survive there. The two things they do need are mana and solitude. Antartica is just the place for both.
The South Pole offers one of the two most concentrated leyline convergence points. As a place for solitude, the North Pole has already had too many mortal expeditions trying to reach the 'top of the world'. No one wants to go to the bottom. The Shades needed a place where they could channel the mana into one central location without their operation being discovered by the mortals.
Their citadel, Moiety, was formed from a unique hexagonal ice crystal that is perfect for conducting the magical essence. The crystal itself emits mana as a natural light source. Moiety, a word meaning kinship for two divided cultures, also serves as the neutral ground where the Light and Dark Shades play out their politics regarding the mortals. It was constructed well before the dawn of mankind, possibly even before the first Other cities.
To deter magical conflict between the two sides, some of the Elders developed a protection pact. The original Shades who had lived full existences and wished not to continue volunteered to be absorbed by the walls of Moiety. Their essences would lie dormant until one of their descendants violated the sanctity of what Moiety stood for. Transgressors are pursued by the Sentinels until they too join the ranks. Contact with a Sentinel causes the Shade to 'burn out' as though he/she had cast an incredibly powerful spell. Normally, any Shade who burns out simply disperses. The residual essence of a Shade inside Moiety becomes a part of the pact. In essence, violators become the new defenders.
It is unsure exactly how big the city is. Moiety has skyscraping spires but an endless
[You must be registered and logged in to see this link.]. Who knows what other deals are made outside the negotiation chamber? Each Shade has his or her own suite in Moiety that can be decorated to their tastes. Just because they have no need for material objects does not mean they have to spend eternity in a drab environment. Each suite is carved from the same crystal, and therefore under the protection of the Sentinels to prevent assassination attempts. Moiety is not a prison, just a place for the Shades to escape confinement as permanent energy sources for the mortals.