The Final Descent

Background
''I've stumbled across Crescius Caerellius inside of Raven Rock Mine. He's convinced that the remains of his great-grandfather, Gratian Caerellius, are at the bottom of the mine and that the East Empire Company has falsely designated his ancestor's death as an accident. He's tasked me with exploring the mine on his behalf to locate the remains, and perhaps discovering what killed Gratian Caerellius.''

Raven Rock Mine
After entering Raven Rock Mine, Aphia Velothi and Crescius Caerellius can be seen arguing about venturing into the mine.

Crescius: " Damn it, woman! I said leave me be!" Aphia: "Crescius, last time you explored the mine you almost fell to your death. I'm not spending the rest of my days as a widow!" Crescius: "And I'm telling you that I'll do whatever it takes to find my great-grandfather's remains. He's down here, I can feel it." Aphia: "That was almost two centuries ago. There may be nothing left to find." Crescius: " Just let me go, woman!" Aphia: "Crescius, you're an obstinate old fool and you're going to get yourself killed."

After talking to Crescius, the quest starts.

Head down into the mine. Follow the path until a platform with a cave to the left side is encountered. Here lives a Skeever and lies a skeleton. Follow the path and a cave can be seen to the right. This cave contains some minor loot and a Frostbite Spider. Now follow the path across the wooden platforms. Another Frostbite Spider is encountered here. Head down the stairs to find another Frostbite Spider at the end of the stairs. Be careful, inside the next corner is a fire trap. Follow the path and go down the next set of stairs. Break the wood at the end of the stairs and enter. There's an Expert locked East Empire Company Strongbox on the chest next to the iron gate.

Now unlock the iron gate with the Raven Rock Mine Key and head inside. Follow the path until water is encountered. Here live several Draugr. A chest can be found in the left crevice after entering the room with water. The next corner contains a trap. Turn around the corner and head up the stairs. Follow the path. Two thrones can be seen in the next room, with the left one containing a Draugr. Walk around the thrones and through the door at the end.

The next room contains a lot of Draugr sitting on thrones. To the left side of the room sits a Master locked chest. Go through the door at the other end of the chamber and head to the right. A Stalhrim deposit can be found in the Draugr crypt on the left. However this can only be mined if in the possession of an Ancient Nordic Pickaxe. Head further down the path to find a Alchemy Lab with all sorts of ingredients, including some added by, specifically two Netch Jelly which are needed for a miscellaneous quest to retrieve five of them for Milore Ienth.

Head further but beware of a lightning trap at the place with two torches. Head into the water and open the door on the right. The next room contains Draugr again. In the waterfall, there's a door leading to Bloodskal Barrow. Inside you will find, two Urns and a Stalhrim deposit with a searchable Draugr under it. Now head back and go upstairs. To the right, after going up the stairs is the door that must be opened. The button for that door can be found at the opposite of the chamber. Don't forget the Expert locked chest beneath the arcane enchanter. Now head through the door. To the left is a chamber with a spell tome for Ice Spike on a pillar. Head right and go upstairs. (Adept level chest under stairs). Watch out for the lightning trap at the end of the chamber. Head through the already opened wooden door and go through the walkway. Watch out of the pressure plates after walking through an already open wooden door. Open the door at the end of the walkway to find an Adept locked chest behind it. Turn around and head right into the little alcove.

The next room contains the destination. Jump down and follow the water. At the end, there's a chest. Now head to the objective and take Gratian's Journal off of his corpse. Read the journal for the optional objective.

Equip the Bloodskal Blade. Do not stand right in front of the door, but slightly back, on the stairs. When doing a power attack, a red beam will come out of the blade. If doing a horizontal attack(done by moving your character to the side while doing a power attack), a horizontal beam will come out, and for vertical a vertical beam will come out. From the stairs, aim the reticle at the glowing red fissures found at the left and right sides of the door. Do this with a heavy attack. First horizontally, then vertically, and then horizontally again. The sections of the walls will alter themselves along with the red fissures; keep aiming your reticle and using the same pattern on the red fissures until each side has no visible red fissure left. Finally hit the door vertically with a heavy attack with the reticle aimed along the new, centered red fissure. Enter the unlocked door and head through the swinging blade trap. Hit the lever at the end of the hallway and go through the door. In the middle lies a chest. But this appears to be a trap, because it only contains two gold and spawns the Dragon Priest Zahkriisos.

Zahkriisos is able to spawn Seekers to his aid. He can use an extremely damaging lightning spell. After defeating him, head to the Dragon Word Wall to learn the first word of Dragon Aspect. Turn around and take the second exit. On a stand lies a Black Book. Reading this will send the Dragonborn to Apocrypha.

Apocrypha
Walk forward but watch out for the tentacles coming out of the water to hit the Dragonborn. Walk forward and kill the spawning Seeker. This starts the quest Black Book: The Winds of Change.

Raven Rock Mine (second time)
After completing the quest Black Book: The Winds of Change, the Dragonborn is teleported back to the place where the black book was first picked up. Look for a chest at the left side of the room. Head up the stairs and open the door to Bloodskal Barrow. Activate the chain on the left side to open the stone door. Kill the enemies and follow the path. Around the corner is another enemy. Head through the door to Solstheim. Kill all enemies in both towers. Don't forget the Adept locked chest on top of the second tower. Now fast travel to Raven Rock and return to Crescius Caerellius. He'll give a reward of 500-750 when the journal is handed in.

Journal

 * Speak to Crescius Caerellius
 * Retrieve Gratian Caerellius's Journal
 * Escape Bloodskal Barrow
 * (Optional) Read Gratian Caerellius's Journal
 * Return to Crescius Caerellius

Bugs

 * The Dragon Word Wall may not give any words of the shout Dragon Aspect.
 * Ebony Ore may not spawn in the mine after the quest has been completed.
 * Upon leaving through the door to bloodskal barrow after returning from Apocrypha, a part of the tunnel will disappear and you will fall through the floor. Can be fixed by going back through the door and re-entering.