...
In
the Enclave setting, planes are, supposedly at least, the quintessential, unending ever-different Farthest that blurs into the Enclave in every place. A wrong step and you may be Lost in the Farthest City, Library, Forest, and so forth.
Lore of the Farthest
"The Datarii call the place beyond all places "the Farthest." The long-departed Draugh, from whom the Datarii inherited myths, fragments of language and little more, called it by this and many other names.
Every place in the Enclave borders the Farthest, or so the Datarii say. Forest, field, library, inn, temple and open land all lead into the Farthest - endless, increasingly strange extensions of the border that led you there. No wizardry is needed to enter the Farthest, and the most common of folk must exercise care in their daily tasks lest they stray too far from the familiar and lose their way.
White-bearded Ammanders first wrote of the Farthest as the "Quintessential Realms," showing curiosity and understanding beyond that of the Lost Magi of the Vanished Isles. The sages hold that certain thresholds must be reached before the Farthest opens up like a rare flower to Visitor and Trespasser alike. The borders of the Farthest are most tangible in large and intricate buildings, the densest of forests, most frequently tilled fields, the busiest of marketplaces and docks."
The
Ten Thousand Gates setting is a far more straightforward convulsion of planescape-done-my-way.
From the Vessel of Books Yet Unwritten
"Creation has many Pillars, you must understand - all are impossible and none may fall. All reverberates from nothing by way of the Song, written by the Book that creates itself from its own tale. All is a lost depth within Amande's venom dream. All is a Demonland in the third crack of Maggat's ill-formed Ull rune. There are ten thousand others, and all are true and impossible. It is a majesty, I feel, to match other majesties that hold sway above the Pillars.
But time is upon us, and a dry wind rises. I am sorry to say that I have no way back for you from the Pillars, but I do have a way forward. Back for me, of course, forward for you. Ah, Leli, let me show you - it is easier. See now, the far side of an Undecided Gate, a folding and rather ramshackle affair as such go, but a most useful traveling companion.
Why, because it does not know where it wishes to lead, of course. There are many Gates in the City of Ten Thousand, and there will always be those that grow bored or shiftless. Hurry, hurry, through you go - folding up the Tailkeeper's Gate is good deal harder and more time-consuming than it looks, and I am not desirous of an audience with the Hunger for Knowledge. You'll have little need of ax and shield, Ulvath - take them as you will, but your nature is fierce enough for most in the Tailings."
Reason
Principia Infecta