The Planes of Oblivion are the dimensional planes which are home to all the daedra. Each of these planes can be very extensive; Molag Bal's plane is described as being a replica of all of Nirn, and Hermaeus Mora's is infinite in size.
Each prince's plane may have a more specific name, for example: Apocrypha for Hermaeus Mora's, Coldharbour for Molag Bal's, Moonshadow for Azura's, Quagmire for Vaermina's. Each plane is supposedly very different in appearance, depending upon the nature of the prince who rules it. They can range from beautiful to desolate; some may not even resemble worlds as we think of them, containing nothing but dust and smoke, or changing constantly.
Oblivion is often associated with tales of Hellspawn and most forms of Destruction (especially fire), and is likely known as Hell, or the home to demons. This image is only accurate for the planes of daedric princes known for destruction, such as Mehrunes Dagon and Molag Bal, as the Daedra are not actually demons, only sentient beings who do the bidding (often destructive) of their respective masters.
 Ogres Tooth Mountains
The Ogres Tooth Mountains are a range of mountains on the island of Stros M'Kai in the kingdom of Hammerfell. They are found to the west of the island's main town and take up roughly a third of the available land area. Despite their dominant presence on the island, they are generally barren and uninteresting, inhabited mainly by those seeking to hide.
 Old Ebonheart
Old Ebonheart is a city on the mainland of Morrowind, along the southern coastline of the Inner Sea. It was once home to a gladiatorial team known as the Reavers. Originally, Ebonheart was to be the capital of the Province of Morrowind, but for unknown reasons it split into two separate city-states, which would become known as Old Ebonheart and Old Mournhold respectively. The two cities were great rivals, and Old Ebonheart lost its political power when Mournhold was rebuilt after its destruction by Mehrunes Dagon in 1E 2920 and declared the capital. The city was further shamed when the Staff of Chaos was entrusted to Mournhold. It is often assumed that Sotha Sil's Clockwork City is located somewhere beneath Old Ebonheart.
During the Imperial Simulacrum, the city under King Casik was at war with Firewatch. The Eternal Champion came to the city searching for the location of Dagoth-Ur. King Casik, who possessed the Anvil of Mithas, offered the hero aid in return for the Hammer of Gharen, the only object strong enough not to shatter when used with the Anvil. The Hammer had been lost in the nearby dungeon of Black Gate, southeast of town. When the Hammer was used upon the Anvil, the ringing would reveal the long lost entrance to Dagoth-Ur. The hero recovered the Hammer—which King Casik used to create the finest weapons and armor in the realm—and learned the location of Dagoth-Ur, which contained the final piece of the shattered Staff of Chaos.
The name of the city was adopted for the new Imperial capital of Vvardenfell, Castle Ebonheart, built sometime after the island was opened for settlement in 3E 414. Due to Old Ebonheart's proximity to Vivec City, it can be assumed that the falling of Baar Dau and the subsequent natural disasters and Argonian invasion in the early Fourth Era caused great damage to the city, perhaps fatally. Umbriel likely passed over the city circa 4E 40, which would have turned any remaining populace into undead.
 Old Hroldan
Old Hroldan (also spelled Old H'roldan, Old Hrol'dan, H'roldan, as well as AHROLDAN in the language of the dragons) was a settlement in southwestern Skyrim. The Pocket Guide to the Empire, 1st Edition, stated the town was in High Rock. It had been taken over by the Witchmen of High Rock before Tiber Septim famously reclaimed it in the late Second Era at the age of twenty.
Reclaiming Old Hroldan from the Witchmen, or Reachmen, was something of a pastime, as an ancient property record refers to "H'roldan" as "A Spacious Wooden Hall and Pasturage, recently Seized from the Reachmen. Silver and Iron as Tribute from the Natives." Other records note that in 1E 2801, Emperor Kastav of the Reman Dynasty ordered hostages to be seized from the town to ensure the jarls met conscription quotas.
Though once a walled and gated city, in modern times, the "town" is simply the Old Hroldan Inn, a resting place for travelers in the Reach. The inn, which is wedged between ruins, mountains, and rivers, boasts to its patrons of harboring Tiber Septim the night he arrived. Recent sightings of ethereal warriors at the inn may lend some credence to the claim.
 Orange Road
Orcrest is a city in northern Elsweyr, south of Riverhold. It was once the home of a gladiatorial team known as the Silent Ones. The noted Khajiit tapestry maker Cherim is known to have lived there towards the end of the Third Era.
Orsinium (which literally translates to "Orc-Town" in Aldmeris) was the city of the Orsimer (Orcs) and the provincial seat of what was considered the Orsinium Area. It has been sacked and rebuilt many times. It was located on a mountain between the regions of Menevia and Wayrest in High Rock, and has reemerged between Hammerfell and Skyrim.