Most Tamrielic cosmologies divide existence into several broad realms, the most important of which are Aetherius, Oblivion, and Mundus.
Mundus is the mortal world and the plane in which Nirn exists. Oblivion contains the realms of the Daedric Princes and countless lesser spirits. Aetherius is associated with the source of magicka, the heavens, and the realms of many divine or ancestral beings.
These divisions are useful, but they do not represent simple physical places separated by ordinary distance. Travel between them is magical, spiritual, or metaphysical.
Mundus is the mortal plane created through the actions of the et'Ada.
Nirn lies within Mundus, along with the structures and celestial bodies associated with mortal existence. Unlike Aetherius or most realms of Oblivion, Mundus is defined by limitation.
Mortals age, die, hunger, travel through space, and experience time in an ordered sequence.
The Aedra are traditionally believed to have sacrificed part of their power during the creation of Mundus, binding themselves to its existence and natural laws.
Aetherius is generally understood as a realm of pure magical and spiritual energy beyond Mundus.
The sun and stars are commonly believed to be openings through which the power of Aetherius enters the mortal world.
Because of this, Aetherius is closely associated with magicka.
Many religious traditions also place divine or ancestral realms within Aetherius. Ideas concerning what happens to mortal souls after death vary by culture, but several peoples believe worthy spirits may eventually reach places connected to Aetherius.
The god Magnus is closely associated with Aetherius and the structure of Mundus.
According to common tradition, Magnus served as the architect of creation but withdrew when he realized the cost of the project.
His departure created the great opening seen as the sun.
Other spirits who fled with him became known as the Magna-Ge, and their departures created the stars.
Through these openings, the energy of Aetherius continues to flow into Mundus.
Magicka is not merely an unusual substance or resource. It is part of the structure of the world.
Living beings can draw upon it to alter matter, energy, perception, memory, distance, and other aspects of reality.
Cultures differ greatly in how they understand this power. Altmeri scholars may describe it through formal magical theory, Ayleids through celestial principles, Chimer through ritual and spiritual practice, and Dwemer through mathematical and tonal models.
Despite these differences, most traditions agree that Aetherius is closely connected to the source of magical energy.
Oblivion is the collective term for the vast realms existing outside Mundus and below or apart from Aetherius in most mortal cosmologies.
It contains countless planes rather than a single uniform world.
Many of the best-known realms belong to the Daedric Princes, each of whom shapes a realm according to their own nature and sphere.
Examples include Coldharbour, the Deadlands, Moonshadow, and the Hunting Grounds.
These realms can differ completely in geography, natural law, inhabitants, and the passage of time.
A Daedric Prince's realm is closely tied to the Prince itself.
The landscape may reflect the ruler's personality, sphere, and desires. A realm is therefore not simply territory owned by a Prince in the same way a mortal ruler owns land.
The relationship is much deeper.
Daedric Princes can reshape portions of their realms, create structures, manifest servants, and impose conditions impossible in Mundus.
Mortals who enter such realms remain subject to the rules of the plane they have entered.
Not every part of Oblivion belongs to one of the major Princes.
Lesser Daedra, independent spirits, forgotten powers, and unusual entities may control smaller planes or territories.
Some realms are little more than isolated pockets of existence. Others may be large enough to contain settlements, landscapes, or civilizations.
Most mortal scholars know only a fraction of what exists beyond Mundus.
The Void is often described separately from Aetherius, Oblivion, and Mundus.
Its exact nature is disputed.
Some traditions associate it with emptiness, nonexistence, Sithis, or the spaces beyond ordered creation. Others use the term more loosely for regions outside known reality.
The Void should not be treated as simply another Daedric realm.
It represents a concept that many cultures understand differently and often fear.
Travel between Mundus and other planes is possible but dangerous.
Conjuration can briefly summon Daedra into Nirn, while portals may allow mortals to enter Oblivion. Powerful rituals, artifacts, divine intervention, or unusual locations can create more stable passages.
Travel to Aetherius is considerably rarer and often described through religious or mystical traditions rather than ordinary magical practice.
The boundaries between planes may also weaken around ancient ruins, magical disasters, or places associated with powerful spirits.
The most common mortal interaction with Oblivion is summoning.
A conjurer may call a Daedric being into Mundus and bind it temporarily to service.
This does not usually mean the Daedra has been permanently removed from its home realm. When its physical form is destroyed in Mundus, its animus generally returns to Oblivion and can eventually reform.
This makes Daedra fundamentally different from ordinary mortal creatures.
The fate of mortal souls varies according to religion, circumstance, and supernatural influence.
Some traditions describe souls passing into ancestral realms or regions of Aetherius. Others believe spirits remain near Nirn, enter culturally specific afterlives, or become bound to particular powers.
Daedric Princes can also claim or receive mortal souls through worship, bargains, curses, or other means.
Because these accounts differ, no single explanation of death is accepted throughout Nirn.
Mundus is not completely open to the surrounding realms.
Cosmic and divine barriers limit the ability of powerful beings to manifest freely within Nirn.
These barriers are not absolute. Daedra can still appear through summoning, cult activity, artifacts, weakened boundaries, and direct intervention.
During the Merethic Era, such encounters are rare enough to inspire fear but common enough to be treated as genuine possibilities rather than superstition.
Different peoples understand the planes according to their own traditions.
Altmeri scholars usually emphasize the relationship between Aetherius, divine ancestry, and the loss represented by mortal existence.
The Chimer accept direct interaction with selected Daedric Princes as an important part of religion.
Khajiiti theology incorporates the various realms into a complex divine family and lunar cosmology.
Dwemer scholars are more likely to study planar boundaries as structures that can be examined or manipulated rather than matters requiring worship.
The same realm may therefore possess very different meanings depending on who describes it.
During the Age of Myth, Aetherius and Oblivion are not abstract ideas known only to theologians.
Daedric cults communicate with their patrons. Conjurers summon beings from other realms. Ancient sites preserve portals or planar disturbances, and divine or supernatural encounters remain part of recorded experience.
Even so, most inhabitants of Nirn will never personally enter another plane.
For ordinary people, these realms exist at the uncertain boundary between religion, scholarship, magic, and direct supernatural experience.
Mundus remains the mortal center of that larger reality: limited, dangerous, and shaped by powers that extend far beyond Nirn itself.