The Endless Labyrinth of Mazek:

The Endless Labyrinth of Mazek is the final of the thirteen realms within the system (the primary realm being the first), and it is a most confounding place to be, even for most of its residents.  Mazek is made of two parts, the surface which stretches in all directions, some say to eternity, and The Undermaze, which is its dark twin, underneath Mazek itself.  Gravity pulls to the center between the two, but the realm seems to be a multi-leveled plane reaching out further than any have gone to search for an edge.  Both sides are covered with shifting walls and passages so ancient that few references to their creators exist even, and the materials themselves require the most powerful of spells to even damage, let alone crumble, yet some areas are more ruinous than others, especially in The Undermaze.  The surface of Mazek has libraries and great clockwork machines put there by its earliest known caretakers that claim to have found it abandoned, The Pagalen.  They are a mysterious race who few have seen outside of their large robes, but they tend to the acquiring of knowledge to those that seek it, typically allowing any access, though some knowledge must still be earned, regardless of their apathy to its usage outside of Mazek.  There are isolated cities within large open sections of Mazek, though they are widely spaced with no certain path that will always one to them.  The Undermaze, on the other hand, seems to be largely controlled in sections by various individuals or groups who insist that despite all the beastly threats, traps and other dangers, more answers are to be found there about Mazek and the other realms.