Arniel's Endeavor

Background
After completing Hitting the Books, asking Arniel if there is anything you can assist with will begin the quest. This quest has four phases. Speaking to Arniel Gane of the College of Winterhold will reveal that he is working on a secret project and requires the Dragonborn's help.

Part one – Dwemer Cogs
Arniel will first ask the Dragonborn to find ten Dwemer cogs. Initially, he will not say what he wants them for. This quest may be started either prior to receiving the quest "The Staff of Magnus," or after that quest has been completed. After obtaining the cogs head back to the College.
 * The Dwarven Storeroom, which is located just outside Mzulft, has four inside.
 * Mzulft itself, accessed in the quest "Revealing the Unseen," has many more than ten. Some are in containers or on tables, while others can be looted from defeated automatons.
 * The Dwemer Museum in Markarth (Understone Keep) has roughly fifteen. Head right as soon as the museum is entered. There are four under a novice locked case and another ten just lying around.
 * Six cogs can be found in the Tower of Mzark. Five are behind the device used during "Discerning the Transmundane." The sixth is in the room that connects to Blackreach on a shelf.

This part will become available after the quest "Good Intentions" has begun. Before that, he will not speak about the Dwemer Cogs at all.

Part two – Warped Soul Gem
After turning in the cogs to Arniel, he requests that Enthir be asked about delivering some purchased goods. After a discussion with Enthir, the Dragonborn is tasked with finding a staff (the Staff of Tandil) at a random location (some are listed below), and returning it to Enthir as payment for a Warped Soul Gem that is warped beyond the ability to be able to capture a soul.

Known locations of the staff include:
 * Boulderfall Cave
 * Brittleshin Pass
 * Fellglow Keep
 * Ilinalta's Deep
 * Cragwallow Slope
 * Morvunskar
 * Falkreath Watchtower (crossroads)
 * Harmugstahl
 * Yngvild
 * Rannveig's Fast
 * Boulderfall Cave
 * Ansilvund
 * North Brittleshin Pass
 * Hob's Fall Cave
 * Southfringe Sanctum
 * Movarth's Lair
 * Sunderstone Gorge
 * House of Clan Battle-Born in Whiterun (behind the locked door)

Part three – Dwemer Convector
This part of the quest cannot be started until the quest "The Eye of Magnus" is complete.

Upon speaking to Arniel again, it is discovered that his project is going terribly. He claims to have forgotten to take into account the heat gain and has consequently destroyed his only working model.

It is at this point that he reveals he is attempting to discover how the Dwemer disappeared "instantly, and completely" by recreating the event. The parts the Dragonborn helped recover were made into a Dwarven convector, which broke during his last attempt to recreate the event. When asked if he wants to build another, he says that he would rather have the Dragonborn find the convectors, scattered throughout Skyrim, made by the Dwarves themselves. Arniel Gane then teaches the spell required to heat the convectors (a novice Destruction spell). Three seconds burn with the spell is all that is needed to heat the soul gem. Arniel postulates that by doing this, the Dwemer may possibly be contacted again.

The locations of Dwemer convectors are marked on the map, and can be fast-traveled to.
 * Two northeast of Markarth.
 * One just north of Deep Folk Crossing, just beyond the north gazebo and over the hill.
 * One due east and across the river from Druadach Redoubt.
 * Two near Mzulft.
 * One is in the Dwarven storeroom south of the arrival point when fast traveling to Mzulft.
 * The second is inside Mzulft, in the first room after the hall on a table.
 * One west of Shor's Stone and north of Autumnshade Clearing.
 * One south of Ivarstead.
 * One at the Ruins of Bthalft.

Upon completing this part of the quest and returning to Arniel, the Dragonborn is thanked and told that the final piece will be arriving soon.

Part four – Keening
After leaving the College of Winterhold for a few days after dropping off the modified soul gem, conversing with Arniel again will reveal that once again Enthir is giving him trouble. When Enthir is asked about it, however, he claims that this time it is not actually his fault. He says he did not keep close tabs on this package because Arniel set up the delivery himself. Enthir suggests searching for the courier, and directs the Dragonborn to one of the following radiant locations:
 * Autumnshade Clearing
 * Broken Helm Hollow
 * Cragslane Cavern
 * Cragwallow Slope
 * Cronvangr Cave
 * Darklight Tower
 * Darkwater Pass
 * Faldar's Tooth
 * Gallows Rock
 * Lost Knife Hideout
 * Mara's Eye Den
 * Mistwatch
 * Morvunskar
 * Pinepeak Cavern
 * Tolvald's Cave
 * Treva's Watch
 * Uttering Hills Cave
 * Redwater Den

Once the Dragonborn retrieves the package, which turns out to be the dagger Keening, and returns to the College and gives it to Arniel, he will give a brief monologue about what he is attempting to do, and then proceeds to hit the soul gem with the dagger. Eventually, there is an explosion of energy, and his body vanishes (similar to when the Dwemer vanished after Kagrenac used Keening and the other tools on the Heart of Lorkhan) leaving the Dragonborn with a completed quest and a Conjuration spell to summon Arniel's shade.

Trivia

 * Arniel's shade may appear in the College as if he were still alive; he sleeps, talks and walks around as a shade.
 * It's possible to find the Courier before taking the fourth part of Arniel's Endeavor quest, then you have an option to give Keening to Arniel after Enthir reveals the location of the Courier.
 * Keening was a major weapon in . It was used in conjunction with Sunder to destroy the Heart of Lorkhan and stop Dagoth Ur from destroying Morrowind, or, rather, all in Morrowind who weren't Dunmer.
 * If the player collects 10 Dwemer Cogs before talking to Arniel to get the first part of his quest, there is no option to ask what he wants them for, which is the dialogue option to start the quest. Instead, the option will be "I've got the cogs," and as Arniel takes them, the game announces that the "Arniel's Endeavor" quest is finished, even though it wasn't even started.

Bugs
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