Crown Sepulcher

"The Great Kath really liked to be prepared, so he took everything with him. So, being the absolute fucking madlad he was, why not take an entire fortress too?"
-Raihan to the Dawn Squad
The Crown Sepulcher is a pocket dimension and fortress located within a fold of the Ancient Abyss. It is the home of the dor'katha spirit servants, and is considered to be the personal sanctum of the lord of the House of Kath. 
The plane exists in an eternal state of night, and the only light that shines comes from the moons Axet and Avanet -which are perpetually eclipsed- and the lunar asteroid Ang-an. The main landmass consists of a small archipelago of floating islands, which are dominated by a gargantuan fortress known as the Legion's Ascent. The fortress's sheer size makes it more akin to a city, if a city was built to withstand an assault from an entire pantheon of gods. 
Entry to the Sepulcher is restricted to exclusively the dead, and any living creatures that try to enter will find themselves forcibly ejected, and if they persist, unable to leave. 
Rule over the Crown Sepulcher falls into the hands the one who can successfully complete the Legionnaire's Gauntlet, a trial in which a potential aspirant must singlehandedly conquer the entire fortress. Traditionally, only the Kath Lord would be granted the right to attempt the trial, though since the clan's fall, the gates of the Assent have been opened to anyone capable of finding their way into the Sepulcher. Though several people -and some dor'katha- have attempted the trial, only Legion Lord Rendus Arulyy, has ever conquered the trials. 
More recently, since the rebirth of the human Leon Huxley into the Kath demon lord Raihan Zoraskaya, the Quadrumvirate -the four most powerful spirits of the Assent- have abandoned their positions to join their traditional master in the waking world, as well as Legion Lord Rendus, as tasked to them by the Great Kath. 
Though backed by five powerful spirits, Raihan has yet to conquer the Assent, due to his Empyrean Curse rendering his soul too weak to win. He has since set up camp in the gatehouse on the Bridge of Frost, which to its credit is a fortress in-of-itself. 
According to my research, during the Convergence, a spire from the Gatehouse was also transported to a cavern in the Faeweald, making it in essence a double-rift. This spire was later found by Raihan's grandmother Hela in her youth, and was linked to the basement of the Huxley Family house in London, Britain. This explains how the family was able to obtain a variety of basic Kath weaponry, despite not having access to the Ascent.