Planar coterminalities are locations in which the borders between planes are so thin that energies, objects, and even creatures from one plane can easily transit into another.
Description
Coterminalities are frequently highly visible, with noticeable differences from the surrounding landscape. Permanently scorched groundcover may mark a coterminality to the Plane of Fire, while those venturing into a coterminality with the Negative Energy Plane may have their life slowly drained from them. Not all coterminalities are so hostile, however. First World coterminalities, for example, can regularly be located by searching for plants of bright and unusual colors, or shimmering and glowing water and air.
On occasion, creatures from one plane can use a coterminality to travel to another without the use of Planar Shift. This process is highly unpredictable and usually accidental.
Coterminalities are often used by those traveling from other planes to the Material Plane, as they allow for predictable destinations to be targeted, avoiding the inherit randomness of teleportation within the Material Plane.
Examples
The Darkland Warps are planar coterminalities.
The Untamable Lands near Rudamun are the site of a large scale coterminality with the First World.
Exorrhiza is a coterminality taken to the extreme, with the Material Plane and First World literally occupying the same physical space.