The Veil is an interdimensional interstice, a space between spaces, a liminal place that cradles and protects the planes of the universe from each other.
For mortals who enter it, it appears as an endless gray void, filled with a bizarre not-fog that obstructs vision beyond a few yards without actually being visible. Faint glows can be seen in the distance, that seem to correspond to the location of important or intensely magical places in the mortal world. Ten points of light shine above and below a dimensional traveler, piercing clearly through the gray not-fog, which we have been told are the realms of the gods, Old and True, though nobody who has attempted to travel to them has returned. Other, fainter points of light can be spotted sometimes, closer than the godsrealms; they are always to be approached with caution, for they represent places where the Far Realms have impinged into proximity to the mortal realm.
Cosmologically, the Veil exists everywhere in the mortal realm, acting as a metaphysical barrier between it and other planes. Scholars are still arguing about whether the other planes of the universe exist in the same space as the mortal realm, just separated from it by the Veil, or if they’re somewhere else, and distant from the mortal realm in space as well as planar alignment*.* The question is generally regarded as being unimportant and unanswerable, but it continues to be a source of lively conversations in academic circles.
Planes are true worlds, spaces that exist unto themselves. Some scholars believe that they are twisted mirrors of the mortal plane, while others point to the utterly alien nature of some and posit that they’re clearly something other, with no relationship to the mortal realm besides being somewhat nearby in a cosmological sense. The known planes consist of the heavens and hells (listed in the Death & Afterlife page) that lie just on the outer edge of the Veil and the Far Realms that are much more remote from the mortal plane.
Demiplanes are constructed spaces, built by mortal mages or other entities. They range in size from closets to palaces to vast swathes of landscape, but they always have signs of their artificial nature threaded through them. This is specially visible at their edges, where the boundaries of the demiplane are clearly stitched or welded closed to keep the Veil from collapsing it back into the mortal realm. From the few accounts of those who have managed to survive such a collapse, it is a cataclysmic event for anything inside such a realm as it falls apart.
Entering the Veil itself is difficult for mortals, as it requires both advanced knowledge of arcane magics and a place where the boundary between worlds is particularly thin. It is generally much easier to open a Gate to a plane or to assist the natives of another plane in opening a Gate to that realm than it is to open a Gate into the Veil itself. The same forces that let it protect planes from each other resist intrusion into its liminal structure. To use a bad analogy, think of the Veil as a tapestry that divides a room in half; poking a needle through the tapestry, crossing from one Plane to another, is significantly easier than threading that needle into and through the weave of the tapestry, i.e. creating a Gate into the Veil itself.
Once you’ve managed to enter it, traveling through the Veil allows you to avoid much of the intervening geography between two points on the mortal realm. Because the Veil has no topography, only vague clouds of dull gray or glowing not-fog and a subjective sense of up and down, one simply has to walk (or float) straight in the direction one wishes to travel, and eventually you’ll reach your destination and can attempt to reenter the material plane.
Of course, that doesn’t mean that it’s easy, or without its own unique dangers. Monsters roam the endless expanse of the Veil, either native to the liminal space itself or wandering in from another plane, that subsist on the aether within the not-fog and any hapless mortals who find their way there. Getting lost in the Veil is entirely possible, too, as the landmarks are distant and hazy and it’s hard to pinpoint exactly where you are in relation to them; there are a number of stories of travelers through the Veil escaping it half-starved and very far from their intended destination.