The material plane of Yarth is mirrored in both a negative and positive way by the Shadowfell and Feywild respectively. There is a wide Astral Sea that then separates these planes of existence from more distant conceptual planes where celestials, elementals, and fiends emerge. Some say that many of the gods themselves exist in these distant planes, but there is arbitrary and conflicting accounts and evidence depending on the mortal source of any information about what lies across the Astral Sea.

Yarth is crossed by magical veins of arcane power known as “ley lines.” Ley lines are conduits of magical energy that traverse all known corners of creation, serving the same function as the veins and arteries of living creatures. These conduits, connecting geographical and cosmological features both great and small, grant knowledge and power to those who tap into them.

A ley line carries raw magical energy along with psychic impressions and other ambient energy its absorbs from its surroundings. This causes ley lines to seed magical effects, subconscious thoughts, and other supernatural phenomena along their paths, and sometimes creates unusual supernatural effects.

Psychic impressions carried down ley lines can impact the cultural and psychological growth of peoples living along the path of a ley line. Such alignments can cause two civilizations separated by thousands of miles—or even separated by planar boundaries—to evolve along similar developmental paths. Towns built on opposite ends of a ley line may have identical (or sometimes mirrored) street plans and similar histories. Artists living near a ley line may unconsciously convey their ideas to other artists on other planes, creating instances of parallel design.

When a ley line penetrates planes, it can carry influences from one plane into another, making ley lines partially responsible for the appearance of tieflings, genasi, and aasimars in bloodlines that had no prior history of contact with outsiders. This effect is also responsible for some of the propagation of sorcerous power, psychic powers, and other unusual magical phenomena such as haunts and loci spirits.

Like the arteries of a circulatory system, ley lines come in many different sizes. The larger a ley line, the more capacity it has to carry magical energy. The size of a given ley line can change over time, however, and may vary at different points along its length. The size of a ley line generally impacts the strength and kinds of power that can be drawn from it by spellcasters.

As a parallel plane to the Prime Material Plane, the Feywild's geography is similar, though not entirely identical. Similarly, just as the geography was reminiscent of Yarth's, its inhabitants and many creatures existed as fey “echoes” of mundane creatures. Arcane magic runs more freely and powerfully in the Feywild than on the Prime Material Plane. Many of its inhabitants are naturally magically gifted. The Feywild is reputably beautiful and terrifying at once, like a dream or a slip into madness. Sometimes the Feywild goes by another name such as “through the looking glass” or “beyond the farthest star” to emphasize the fact that it is a place of creation, magic, and madness.

The Shadowfell, commonly known as the Plane of Shadow, is a second parallel plane to the Prime Material Plane. connected through occasional portals to the Prime Material Plane. The most striking and immediate impression a visitor to the Plane of Shadow is the lack of color and light. No sun, moons, or stars adorn the vault of the inky black sky. The color appears to have been leeched out of all things leaving nothing but shades of black and white.

The landscape of the Shadowfell is a dark, twisted echo of what exists on the Prime Material Plane. Upon entering the Plane of Shadow, the local features are usually quite similar. A forest or body of water has an eerily similar counterpart in the shadow plane. However, from that starting point the landscape diverges rapidly away from the familiar. On subsequent visits from the same starting point the geography and structures themselves diverges in different ways, making mapping the Shadowfell futile. Landmarks are usually recognizable but altered in some bizarre way. Buildings might be constructed in a different style, built with different materials, at a different location, and/or in any condition from dilapidated ruins to a distorted version of its normal appearance.

Sometimes the Shadowfell goes by another name such as “the upside-down” or “the immutable dusk” to emphasize the fact that this plane is one of unceasing monotony and despair.