Ley lines, also known as interplanar conduits or interdimensional conduits, are invisible, incorporeal network of interconnected tunnel-shaped conduits permeating the fabric of the planes. On a given plane, a ley line manifests as a single point of weakness in its dimensional structure. The form of ley lines, however, as the name suggests, is that of a snaking path that extends beyond the boundaries of a given plane, most often connecting with other ley lines that terminate at other locations on the same plane.
The network of ley lines is structured much like a root system with no end, with “lower levels” of lines connecting both to other points on the same plane as well as other segments “higher up” in the system, which in turn connect with other planes in even the most distant regions of the omniverse.
Ley lines are considered to be the remnants of the creation of the omniverse, formed much like seams of joined pieces of fabric from when the myriad planes were joined together with the astral media.
The most frequent interaction with ley lines is through magisters’ use of them as conduits between the planes, serving as navigable paths of least resistance to realms far away. While these pathways cannot be physically traversed in any reasonable sense of the word, they permit the passage of magical energy from one location to another (typically from one of the Planes of Energy to the recipient plane) either for the purpose of the emission of raw energy or to be shaped and manipulated by a sufficiently skilled mage to achieve a specific, desired effect (including the potential for teleportation through the conduits by particularly advanced magic-users).
Ley lines are closed the majority of the time, expanding open as though a birth canal only when passing energy expands a given stretch of pathway. After the energy has passed through transit, lines rapidly settle back shut, precluding the possibility of an extended unattended connection. However, rarely particularly well-traveled or manipulated (some might say “sabotaged”) conduits may eventually become slow to close, close incompletely, or remain open permanently. Typically, these “malfunctions” manifest only along fairly short stretches between a single terminal point and a junction; between two junctions; or along a single path along a larger branch of a local network. Larger malfunctions have been known to occur, though, sometimes stretching along vast expanses of the ley network, very rarely directly connecting two planes in a permanent link. Such an occurrence, if connected to, say, a Plane of Energy, would prove disastrous for the destination plane as magical energy floods the universe unstoppered.
More typically, though, ley malfunctions serve primarily to vex would-be spellcasters acting in the proximity of the malfunction. While a caster attempting to channel energy through an improperly-closing section of conduit would receive his or her desired payload without any substantial problems (perhaps a small amount of dissonance resulting from the incongruity in navigating between properly-functioning segments into improperly-functioning segments and possibly back again), those who truly suffer from ley malfunctions are those who reside proximate to the terminal point of malfunction (for those malfunctions that abut directly against planar boundaries) and spellcasters attempting to use nearby ley terminal points.
If a caster tries to draw energy through a (fully-functional) local ley line that is connected higher up to a malfunctioning section of conduit, the caster will find his or her magical energy flow particularly weak or almost nonexistent compared to the intended result. The energy summoned forth, instead of channeling completely down the series of functional ley lines, is instead diverted, in part, down the open lines along the way, netting a smaller result in energy for the intended recipient than expected. The diverted energy then pools through the improperly-opened channels, expelling itself either in a (sometimes) subtle leak through lower terminal points (in the case of an isolated malfunction in the upper branches) or abruptly and violently at a single (or small number of) point(s) (in the case of a malfunction at or very near a planar boundary.
Local lines (those nearest planar boundaries) are most prone to malfunction, given that individual terminal points are apt either to be used very infrequently or taxed to the point of overuse, depending upon the presence or absence of spellcasting activity. Deep lines (those far removed from planar boundaries), found far within the astral media, are, in contrast, constantly-trafficked and are, thus, well-reinforced against the possibility of such malfunctions. Particularly well-traveled deep lines even have the capability of accommodating multiple discrete payloads to their proper locations with minimal possibility for error or mischanneling. Just as local malfunctions can make life miserable for those within its area of effect, though, the prospect of a deep line malfunction, however unlikely, would net catastrophic results for vast expanses of the omniverse, potentially rendering multiple planes magically useless and/or dragging their denizens down in a rain of magical chaos.