Levels of The DeepIt's not much, but at least it's something.

Here we have a very general outline of the levels that will make up The Deep. A lot of unique stuff here and a lot of me wanting to bring sections of the Forgotten Realm's Undermountain into the Elder Scrolls setting.
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The Upper DungeonsThe Upper Dungeons Level of The Deep shows the influence of a variety of builders over the centuries. The Thieves' Guild constructed Grayquay Outpost and the series of stairs, shafts, and passages that connected it through the Upper Dungeons to the Storeroom Level and the Maze Level. Various mining operations have been started on this level but never completed. This level has long been used by the Northern Legion as a dumping ground for undesirables. It is also known as the Temple Level, for the many temples of Daedra and the Divines that have been constructed here over the years, and the Tomb Level, for the many lords and kings that have been interred herein as well. As explorers of The Deep often visit this level, its features are common tavern-talk of Charm. Notable features of the this level include the Hall of Many Pillars, Grayquay Outpost, the Hall of Three Lords, the Hall of Sleeping Kings and The Groan.
The Storeroom LevelOver the centuries, unknown factions have excavated the rough stone caverns and mining tunnels left here by the Dwemer and the Ayleid to use in storing their acquisitions and magical experiments. Notable features of the Storeroom Level include the Doomgate, the Hemwatch and Lord Hund's Tomb.
The Maze LevelThis level contains five major features of note - the deep elf outpost of Morbala (once an Ayleid outpost), the Lair of the Umber Hulks, the Maze of Madness, the old thieves' hold called the Outpost of the Bloody Hand, and the winding channels of the River Graymurk. Morbala is linked by a series of portals to the deep elf city of Mala Nagasel, which lies deep down in the Tal-zal's Gauntlet level. The Maze of Madness is thought to be a creation of the Ayleids and is magically stocked with ravenous minotaurs and magic traps to confuse and trip up the unwary.
The DeepswampsLocated deep beneath the village of Charm, the Deepswamps is a largely unexplored level between the Maze level and the Deepseas.
The DeepseasThe Deepseas have numerous waterway connections to the Abecean Sea and Niben Bay. This level once housed two major mining operations of the Dwemer. Nigh-endless mining tunnels stretch outward in several directions, following now-vanished veins of mithril. Only numerous Dwemer-built locks and pumps prevent the ocean waters far above from seeping down and wholly flooding the level.
Known for the massive lake called The Glimmering and the River Saradel, which winds through this massive level, The Deep's fifth level consists of two major sections. The southern third of the level consists of the remnants of an ancient Ayleid enclave known as Pellani Auran, now split by a massive cave-in leading to the city of Khare and the ruins of Elkhazel Aza. The northern two-thirds of this level are largely undocumented. The most notable feature of the northern area is the Pit of Ghaunadaur, a miles-deep shaft that leads from the Prime Material Plane (the Mortal Realm) into an intermittently existent planar breach that is said to lead to planes of existence below Oblivion, into the Abyss.
The Farms LevelThe sixth level of The Deep contains farms no surface dweller would recognize. Mighty Ayleid magic brought the River Saradel to this level, where it links huge caverns in broad, sweeping curves, and is navigable by barges and numerous bridges. In these caverns, slaves and servants of the deep elves, deep orcs, and other races of the depths produce slimes and algae for food. There are many magically self-contained Ayleid farms here too, and their produce is teleported to "feed-bin" rooms throughout the the depths (rooms known to resident monsters as "watering-holes").
The Deep's privies are also rinsed by magically pumped or redirected water into miniature portals that bring their contents to the farms. The dung-heaps produced by this process are inhabited by many types of foul scavengers. All of these farms are quite valuable, as there are few large sources of good food underground; thus, all are heavily guarded. The deep elves and deep orcs have both used fearsome monsters as guardians, including giant spiders, minotaurs, golems, beholders, and even wilder creatures.
A large, eerily dark lake at one end of the level supports a deep elf "fish factory," an important industry, heavily guarded to prevent food-raids from other creatures of the The Deep. An island in the middle of the lake is piled deep in dung, offal, carrion, and other refuse that finds its way down long, twisting garbage-shafts from Khare.
The Terminus Level The Terminus Level is a mix of Dwemer-built chambers, still-producing mithril mines, and vast natural caverns. The Terminus Level connects the above heart of The Deep to the even more dangerous lower levels and is the only route further downward at this depth.
The WyllowwoodThe altmer wizard, Kardryn Aundae "the Stone Shaper," created the Wyllowwood over three centuries ago for his beloved, a bosmer druid named Wyllow. Set in a cavernous region carved by a tributary of the River Saradel, this level is dominated by the Wyllowwood, a thriving forest nourished by sunlight filtered through a massive portal in the "sky" above. Other notable features include a temple of Arkay and a long-abandoned lakeside village built by the the thieves' guild.
The Lost LevelEntombed in solid rock, the Lost Level is almost inaccessible, and its primary egress is said to be a portal guarded by the "Ring of Death," a waiting ring of undead beholders. The Lost Level is divided into three sections - a temple of Molag Bal and the ancient Ayleid ruins of Haelia Rielle, a beholder prison, and a massive cavern carved by a branch of the River Saradel and now split by an earthquake-caused tremor.
Tal-zal's Gauntlet Tal-zal's Gauntlet is a level built by the deep elves soon after their initial entry into The Deep and the area included living quarters and a warrior academy. Tal-zal transformed these chambers into a trap-filled gauntlet haunted by giant spiders, undead, and other horrors. Although the monstrous mage has long, long ago abandoned this area, it is now home to a major city of the deep elves, Mala Nagasel.
The Runestone LevelNot much is known about this small level located between Tal-zal's Gauntlet and The Terminus Level. It remains largely unexplored though rumors state it is linked to Umbragloam Hold by multiple small, twisting passages.
Umbragloam HoldThis level is the deepest known level of The Deep. It may or may not be connected to even deeper levels. There are no known records of the areas contained here.