Extraplanar Weak Point
In most multiversal models, including the Standard Multiversal Model, Yendalism, and the multidimensional web model of the elven philosopher Avariel, the planes are thought to exist in a complex space that cannot be straightforwardly depicted, where distance between planes is not a simple linear measure. Thus, as metaphorically described by Gaius Devarro, there are always “places in our physical world of the Material Plane where the walls between planes are thin and you can hear the shouting of the worlds next door if you listen.” These are typically known as Extraplanar Weak Points.
These are not portals: as described by the foundational work On Metaphysics, portals between planes are themselves infinitely long and infinitesimally short at the same time, tunnels that defy logical explanation. Indeed, careful experimentation recorded in the seminal work On the Nature of Extraplanar Travel showed that it is no easier to traverse across planes at extraplanar weak points than elsewhere. However, there are many recorded tales of strange magic being common at these places, thought to reflect the ability of extraplanar energy to leak across planar boundaries in places where the planes are unusually close together. Indeed, extraplanar weak points are often deliberately exploited as sources of planar energy for magical workshops.
Many planar geographers have sought to understand the properties of these extraplanar weak points. Ishara Venn, studying elemental vortexes, claimed they were akin to long-lasting elemental vortexes: connections caused by action on the Material Plane that draws extraplanar energy and in doing so draws a particular plane closer. Others, including the elven philosopher Avariel, have argued that most extraplanar weak points are scars of the Riving, places where the planes were never fully separated by the Divine Presence. And the lizardfolk epic The Endless Currents describes the Tharzen Anzinakoa, the Firstborn of the Lizardfolk, as weaving strands of energy and spirit into the Material Plane, knitting the multiverse together with threads of connection to prevent the shattering of the cosmos, although whether this is intended to represent a metaphysical truth or a metaphor is never clarified. The exact nature of these extraplanar weak points remains an unsolved mystery in planar geography.
Planar Dualists and Extraplanar Weak Spots
Followers of planar dualism, unlike most other metaphysical cosmologists, argue that extraplanar weak points have nothing to do with planar geometry. Instead, they have to do with energy flows. Planar dualists often speak of the metaphor of the sea of magic and the sky of Soulstuff, forming the floor and ceiling of the multiverse. In this model, extraplanar weak points represent energy currents, akin to the “rivers” of Ley Lines, that flow between planes, and are thus best thought of like a metal poker that becomes hot along its entire length when left in the fire too long. Each extraplanar weak point represents the Material Plane terminus of the metal poker, the far end sitting in the furnace of another plane.