There are multiple landmarks from TES IV: Oblivion that have been recreated in the Cyrodiil zone of The Elder Scrolls Online, but are not normally accessible. They are sometimes shown on the map, but not named in-game, so are listed here by their names from TES IV. Most of them are found around Niben Bay in the southern part of the zone, or in City Isle in the central part.
If one goes past the intended boundaries, they will most often be teleported back to one of their Alliance Gates.
The Arcane University is the former headquarters of the Mages Guild that was established in an ancient Ayleid district of the Imperial City, on the southeast part of City Isle. Though the outside cannot be traveled to, the interior is accessed in the Arcane University battleground.
Bravil is a city in the Southern Niben Valley. It is surrounded by slaughterfish-infested waters and is walled off, making it difficult to get inside the city. If one goes to the bridge to the gate leading to the Nibenay Valley on its southern side, they will be teleported back to their alliance gate.
Corbolo Cave is an empty inaccessible cave between Drakelowe Grounds and Mist Morrow Vale. It is within a waterfall that feeds into the Corbolo River. There are a number of rocks and invisible barriers near it, and while one can climb in front of its opening, a barrier prevents entering it.
Crestbridge is a small bridge passing over the Corbolo River, leading to Fort Cedrian and Nibenay towards the east. The western half has a makeshift barricade consisting of crates, wagons, barrels, planks, and stakes. There are also two burnt corpses lying on it.
Fort Aurus is a ruined fort in the Nibenay Basin, found on a cliff overlooking Niben Bay. The waters on its western side are infested with slaughterfish.
Fort Cedrian is a ruined fort on the eastern banks of the Corbolo River. It is found on the north side Crestbridge.
Fort Grief is a ruined fort on an island in Niben Bay, surrounded by slaughterfish. There are many trees on the island, as well as some docks on the western side. A skeleton on a chair can be found here with a paint palette in its arms, in front of a canvas displaying a map of Cyrodiil, likely a hidden easter egg by the developers.
Imperial City BridgesEdit
There are about three main walkway bridges located on the outskirts of the Imperial City, between the various shores of Lake Rumare and City Isle. A friendly captain of the Imperial Legion can be spoken to at each one, while their soldiers fight off Daedric Titans and Daedroths on the bridge. A Dremora Channeler can be found at the end of the bridge before it breaks off halfway through, as there is a Coldharbour-like floating island with an anchor in the center. There are also three minor fortified bridges with windows that are closed off and can also not be used.
Imperial City OutpostsEdit
There are about three outposts located on the outskirts of the Imperial City on City Isle.
Imperial City PrisonEdit
The Imperial City Prison is a district of the Imperial City found on the northeastern shore of City Isle. The interior is accessed in the Imperial City Prison dungeon.
There is a large split drawbridge southeast of Drakelowe Keep with a road leading to its west side. The center of the bridge has been lifted, meaning it is impossible to its eastern part, that leads into the Nibenay Basin.
North Niben Bay IslandEdit
An island in central Niben Bay can be seen east of Bravil, and has a broken boat on its northern side, and an intact boat south of it.
South Niben Bay IslandEdit
An island in central Niben Bay can be seen east of Bravil. It is south of the ship and the northern island.
Niben Bay ShipsEdit
There are a number of ships within Niben Bay. One can be found at the mouth of the Corbolo River, and is seen on the map as a very small brown dot with ripples around. The second one is broken in half, and is on the northern coastline of the northern island in the center of the Bay. The third one is intact, and is found between the two islands in the Bay, east of Bravil.
The Silverfish River is a large body of water that travels through the Nibenay Basin and Valley.
The Waterfront District is a part of the Imperial City found on an island in the southwest part of City Isle, east of Fanacasecul. There are a few ships around it, as well as a number of ships docked in its harbor, with a number of houses located behind the wall. It is surrounded by slaughterfish, though if one managed to get past them they could walk around the inner part of the district, which can no longer be done as a number of invisible barriers were added in a later patch.
It is the only district to make no appearance in the Imperial City DLC (excluding the Arcane University, which appears as a battleground in the Morrowind chapter), however, Clivia Tharn mentions it in a vision in the White-Gold Tower, saying that soldiers must be sent to defend the district.
City Isle, or the Imperial Island, is a large island found at the center of Cyrodiil in the slaughterfish-infested Lake Rumare. It contains the Imperial City, and has a number of bridges connecting to it, but they are all broken and cannot be used. If one does manage to get to the island, the coastline contains many unclimbable rocks that make travelling to the center very difficult. It is also very likely to be instantly killed by the "Imperial Law" environmental damage effect.
The Colovian Highlands are a region found west of the Daggerfall Territory and Chorrol. They are blocked off by a wall of mountains and rocks.
The Nibenay Valley is a small region south of Bravil and the Corbolo River. In Bravil, there is a closed gate on its southern side that presumably leads to the region.
The Nibenay Basin is a region found across the banks of the Corbolo River, blocked off by mountains and cliffs. It can be seen east of Fort Grief, but is very difficult to reach.
The West Weald is a region found west of the Aldmeri Territory, blocked off by a long wall of rock and invisible barriers. There is a wall west of Blessed Water that shields off the region, and the waterfall feeding into Silverscale Pond comes from it. Although the region can't be accessed from Cyrodiil, it can be reached by glitching out-of-bounds in Malabal Tor. This once allowed players to reach Miscarcand and the partially-completed city of Skingrad which have since been removed.