This is the tesseract Shard creates when he becomes a First-of-the-First.
It is created in the memory of lost Quarlangia, as a sanctuary for those with Determination, and a place for second chances. Because the Quarlangians were an apothean race of the First World, Shard believed that their innate advantages over other races would create resentment as it had in the past, and therefore it was best to remove them from the DemiUrge’s universe so that they could live in peace.
Notably, the rules of this tesseract restore those whose bodies have been damaged or destroyed. This allows Clyde and the Quarlangian timeghosts who travel here to be made whole.
Moreover, Gigamuth who come here are changed; they become smaller (though large sized) and their Cronite hunger is purged from them. Essentially, they are a wholly new offshoot of the Quarlangian people. Shard did this because of a deep sense of duty toward the Gigamuth for how the Quarlangians had selfishly used them in the past.
Shard asked Ariadne to bring all willing Quarlangians, timeghosts, and Gigamuth to the Sanctuary.
Notable residents of the Sanctuary are Shard, Serket, Vincente, Ariadne, and Clyde.