Tytherion

A plane used to contain Tiamat's soul following her demise on the Material Plane. Essentially nothingness originally, but has been molded by Tiamat's wrath over the millenia into The Endless Night, a maze of windswept canyons hunted by her draconic minions. She apparently found or constructed a rift between Tytherion and the Shadowfell, as she has been recently discovered to have migrated between the two.