- Many Dwemer parts that can be smelted into Dwarven Metal Ingots which are used to smith Dwarven weapons and armor.
- At least three Centurion Dynamo Cores.
- A Restoration Skill Book called the Racial Phylogeny is found.
- Gems and Soul Gems looted from enemies.
- Several chests with loot.
The Dragonborn will find From-Deepest-Fathoms wandering around Riften's docks. Upon first meeting her, she seems despondent and paranoid, immediately wanting to give the Lexicon over to the Dragonborn, pleading for it to be returned to the Dwemer Ruins of Avanchnzel.
Upon arriving at Avanchnzel, four transparent orange figures will be standing at the bottom of the first large open cave room. These are the 'ghosts' of four adventurers (or "thieves", in their own words, and none of them can pick a lock), who went to Avanchnzel to recover/steal the Lexicon.
They will reappear throughout the quest and the Dragonborn can overhear that the two human characters had little knowledge about the place or item of interest, but From-Deepest-Fathoms and Watches-The-Roots were very familiar with both and persuaded them to stay and complete the job against their better judgement. The two human mercenaries stay, only because the job paid well, but it becomes clear that the Argonians sought out the Lexicon for the knowledge it housed.
Beware of the trap when opening the door on the right in the next room. Continue through rooms and doors, eventually coming to a large room with two Dwarven Centurions on large stone tables.
In the next room, one of the adventurers, Drennen, is lying dead on the floor. He left the group for unknown reasons.
Upon entering the boilery, the three remaining ghosts talk about the lexicon and what to do with it. Moving forward through rooms and corridors, the ghosts reappear before a door and they are in a hurry to reach the Receptacle. In the next room, the Dragonborn discovers the second dead explorer, Watches-The-Roots.
Finally, through the last door, the Dragonborn enters a large room with Breya, the last of the explorers, lying dead on the floor. A Dwarven Centurion is guarding the Receptacle in which to place the Lexicon.
Upon activating the receptacle, the Lexicon will be removed from the player's inventory and open. The Dragonborn will be rewarded with Ancient Knowledge, a permanent bonus. The Quest will now be completed.
Leave by the door behind the Receptacle and go through the barred doors and out to the Avanchnzel Balcony for a faster exit and a locked chest with some loot.
This dungeon is not accessible before the quest has been activated (Dungeon Lock Outs).
- From-Deepest-Fathoms will not appear until the Dragonborn has reached level 14
- Pickpocketing or just taking the lexicon from From-Deepest-Fathoms and then placing it back in her inventory will cause her to still act as though the Dragonborn still has it and will say "No, It's yours now, I won't take it back I won't!," even though she has it in her inventory.
- From-Deepest-Fathoms is the only person it can be placed on.
- From-Deepest-Fathoms is not marked as an essential character so she can be killed if attacked. The Lexicon will still be in her inventory after she dies.
- Stealing the Lexicon only results in From-Deepest-Fathoms turning around and talking as if the Dragonborn has done her a favor and beginning the quest.
- From-Deepest-Fathoms will give the Lexicon to the Dragonborn even if he/she is in the water and not on the docks.
- If any Dwarven weapons, like the Dwarven Bolt, are taken, a letter will be sent from Calcelmo through a Courier stating he wants the Dragonborn to bring one to him in return for a large payment. This will begin the quest Letter from Calcemo.
- It is easy to become stuck in the South East corner of the room in which the apparitions discuss whether the Dwarven automatons were sleeping or waiting.
This section contains bugs related to Unfathomable Depths. Before adding a bug to this list, consider the following:
- Not necessarily a bug, but occasionally, when swimming near the docks in Riften, you will be addressed by From-Deepest-Fathoms, who irritatedly asks why you are bothering her. However, in the subtitles, her name only shows up as Fathom.
- There is a rare chance that in the Avanchnzel Boilery's first ghost encounter, From-Deepest-Fathoms will not say the last line in the conversation and the ghosts do not vanish. When the next few ghosts appear, they do not say or do anything and stay put. This does not affect the quest, but it's also interesting to note that the Dwarven Centurion ghosts show up as enemies on the compass and the real Centurion cannot walk through them.
- Saving before entering the Boilery is advised as it is prone to glitch and lock up while in the loading screen.
- Whilst in the Boilery there is a chance that a Dwarven Spider will spawn under the grated floor in one of the corridors, but it cannot hurt you and vice versa. However, it may stop you from clearing the ruins. To fix this simply open up the console and type 'killall' whilst standing above it, or by using Blizzard while standing directly above it. Another way to easily kill it is using Chain Lightning.
- When entering the first room with the Dwemer Spiders and attacking with bow and arrow, the arrows pass straight through them and they receive no damage.