Cosmology

Aurbis
Aurbis is essentially universe. It is the foundation of everything, including the Void, the un-Void, Oblivion, the Lands of Aetherius, Mundus and the Outer Realms.

Aetherius
Aetherius is a spirit realm where the source of magicka resides. Immortal spirits reside in Aetherius, including ex-mortals who have learned how to become immortal. It exists "beyond" the mortal realm of Nirn, beyond the realm of Oblivion, and even beyond Aurbis. Aetherius is the home of the Aedra, the gods of the Imperial Cult and are the most worshipped creatures in Tamriel, the next closest competitor being the Daedra.

Battlespire
Battlespire is a magical academy that trained elite Battlemages for the service of the Cyrodiil Empire of Tamriel. It is located on the border between the "normal", human dimension and Oblivion, the dimension of Daedra.
The origins of Battlespire are unknown, but at some point in the Third Era the academy was utterly devastated and nearly destroyed by the advancing forces of Daedra led by Daedra Prince Mehrunes Dagon and armed with fearful Daedric Crescents. This assault was aimed to conquer Tamriel and the rest of the mortal world but was stopped by the last surviving graduate of Battlespire who defeated Dagon and closed the interdimensional portal.

Oblivion
Oblivion is the realm inhabited by Daedra. It is the void surrounding Nirn, the mortal plane of existence. The planets, nebulae and other astral bodies in the sky are the mortals' view of the spheres of the Daedra floating in that void. Stars are holes on the inner surface of Oblivion through which the energy of Aetherius shines into the mortal realm. This is also true of the sun, which is known as Magnus. The exception is the constellation of the Serpent, Sithis, which is made up of unstars (through which, presumably, the energy of Oblivion shines into Aetherius).

Nirn
Nirn is the planet. Its name means "arena" or "the battleground" in the Elven language (Ald Ehlnofex). Nirn is also known as Mundus (the "Mortal Plane"), and is located in Aurbis, between the Aetherius (the "Immortal Plane"), and Oblivion. Nirn is named "Mortal Plane" because the species which inhabit it die. The planet is orbited by the two moons Masser and Secunda, while Nirn orbits its sun, called Magnus. The continents of Nirn include Akavir, Aldmeris, Atmora, Pyandonea, Tamriel, and Yokuda.

Continents of Nirn

Tamriel
The name Tamriel is said to mean 'Starry Heart', however, it is also Elvish for 'Dawn's Beauty'.
Tamriel consists of nine provinces, Black Marsh in the southeast, Cyrodiil in the center, Elsweyr in the south, Hammerfell in the west, High Rock in the northwest, Morrowind in the northeast, Skyrim in the north, and the Summerset Isles and Valenwood in the southwest. In addition, the city state of Orsinium is currently seeking provincial status and is located in High Rock.

Akavir
Akavir, or "Dragon Land" in the native tongue, lies to the east of Tamriel and is the homeland of the Akaviri. There are four major races of Akavir: the monkey-breds of Tang Mo, the snow demons of Kamal, the snake-like Tsaesci, and the tiger folk of Ka Po' Tun. In previous eras the Tsaesci managed to invade Tamriel but were driven back. Little else is known about the continent or the people of Akavir, although humans did live there in early ages, but were eaten by the Tsaesci.

Aldmeris
Little is known about Aldmeris. It is rumored that Aldmeris lies to the south of Tamriel. Aldmeris is also called Ehlnofey in Elven tongue. It is the place the Aldmer emigrated from and was said to be completely covered by urban growth. It is possible it is still populated by Aldmer, but all those who had tried to find it have failed. It has also been suggested by some that Aldmeris is a myth, and does not actually exist.

Atmora
Atmora is a frozen, unlivable land. In the Elvish tongue Atmora means means "Elder Wood". Atmora was once warmer though still an icy place, populated by the Nedes, which were organized into clans and fought in civil wars for hundreds of years. More than 4,000 years ago, a man named Ysgramor travelled to the distant continent of Tamriel. He founded the capital city of Saarthal, which was soon razed by the Aldmer, the ancestors of all Elves. Ysgramor retreated to Atmora with his two sons, and raised an army of 500 Nedic warriors known as the Five Hundred Companions, to take revenge against the Aldmer, who were almost completely eradicated in that portion of Tamriel. Ysgramor founded Skyrim, the first human kingdom of Tamriel.

Pyandonea
The kingdom of Pyandonea is series of islands to the south-west of Tamriel. Sometimes regarded as a continent, the islands are covered with rainforests and a habitat for water spirits. It is also the homeland of the Tropical Elves (or "Maormer"). The king of Pyandonea is the immortal Orgnum Thras, a wizard who claims to be God-Snake of Satakal. Three centuries ago, the island broke its alliance with the Summerset Isles, and Orgnum waged war against Tamriel. Potema, queen of the Kingdom of Solitude tricked Orgnum by convincing him that she would assist in overthrowing the current emperor, her half brother, Antiochus. Potema's scheme made Orgnum and his entire attacking fleet begin their assault against Tamriel. When Orgnum's Fleet passes near Artaeum, the homeport of the Psijic Order, a magical storm destroyed the entire fleet including Orgnum. The storm was created by the Psijic Order under the payroll of Potema.

Yokuda
Yokuda lies to the west of Tamriel and was the homeland of the Redguards. It was once a prosperous continent and the birthplace of the Yokudan civilization. 3500 years ago, Yokuda was devastated by a gigantic tidal wave, of which the causes are still unknown today. Some believe that it was caused by the Sloads, but it is more commonly accepted that the continent was in a deadly civil war and the Yokudans used a terrible weapon which poisoned the water and salted the soil of their lands, rendering them useless. Only one small archipelago remains today.
The warrior class of the Yokudans, also known as Ra Gada, or "Forebearers", sailed east to settle down in Hammerfell, where they were known as Redguards. The nobles of Yokuda, the Na-Totambus, or "Crown", chose to remain in Yokuda and were swallowed by the tidal wave. Little is known about the continent or the people before they sailed to Tamriel.

Thras
Little is known about the Coral Kingdoms of Thras, for any explorers that have gone there, have never returned. It is known that Thras is located southwest of Tamriel and that its inhabitants are the sluglike beastmen called Sload. The Sload are a disgusting race of teleportation-loving necromancers.
The Sload Coral Kingdoms have generally followed an isolationist policy, with only limited contact and trade with Tamriel. Therefore their history is not greatly known. The most important event known is when they released the Thrassian Plague upon Tamriel in 1E2200, killing more than half of the population. In response, Tamriel assembled the All Flags Navy that ravaged Thras, killing all the Sload it could find and finally sinking it with unknown magics. The Sload, however, survived, and Thras has since risen again.