Black Books

"Where the Black Books actually came from... no one really knows. Some appear to have been written in the past, others might be from the future."

- Neloth Black Books are tomes of esoteric knowledge found in. They are Daedric Artifacts attributed to Hermaeus Mora.

There are seven different Black Books scattered through the ruins of Solstheim. Three are guarded by the Dragon Priests, Ahzidal, Dukaan, and Zakriisos.

Background
Black Books are esoteric tomes that are magical and other-worldly in nature. When read, they present the reader with exceptionally powerful knowledge that comes with incredible powers which mortals could never conceive. They are Daedric artifacts created by Hermaeus Mora to lure mortals into his service. Some appear to have been written in the past, while others appear to be from the future. They are much sought after as they contain hidden knowledge that grants the reader great power.

The first Dragon Born Miraak came into possession of one book that led him into the service of Hermaeus Mora. Eventually this resulted in him learning how to bend the will of Dov. The Dwemer discovered another book in the First Era. Since the acquisition and usage of hidden knowledge was somewhat a specialty of the Dwemer, they began to study it to reveal its secrets.

Reading
Opening a black book transports the reader into a region in the realm of Apocrypha. Once the region has been traversed, a book awaits on a pedestal. Reading the book grants a unique Power or ability.

However when opening a black book inside Apocrypha, the corresponding region of Apocrypha would not open. Instead the player would be transported back to Solstheim. This can be used to exit Apocrypha at any time without using(reaching) the hidden knowledge book typically set at the end of each Apocrypha scenario. This is especially important in the case of reading Waking Dreams without activating the final main quest At the Summit of Apocrypha because after reaching the word wall for Dragon Aspect, there is no visible exit in form of interactive item while the door behind player is locked.

Black Books can only be read in Solstheim. Attempting to read a black book in Skyrim will result in the message: "A vision of Solstheim swims before your eyes and then is gone." When the message is acknowledged, the inventory closes and the surroundings shake briefly.

Trivia

 * Some followers react to the Dragonborn reading a black book, making such comments as "I can't believe  you do that on purpose", "Not again", "I wish you'd stop doing that", or "That can't be good for you..."
 * Neloth can give the locations of Black Books in the quest "Lost Knowledge".
 * The books remain as quest items after "At the Summit of Apocrypha" and cannot be dropped.
 * A Black Book can be treated as a portable storage container while on Solstheim. Upon re-entering the "Winds of Change" the player is close to a chest and the exit. It is helpful to dump the heavy loot there while exploring, then take it back when near a merchant/permanent storage.
 * The Sallow Regent is likely a reference to Robert Chambers' The King in Yellow.
 * The writing on the Eye of Magnus is very similar of that in the Black Books, although not the same.

Bugs

 * Upon exiting Apocrypha, the sound of paper whirling in the wind will persist. Saving and reloading the game should fix this.
 * Upon exiting Apocrypha from The Sallow Regent or The Hidden Twilight, the burning sound of the darkness will persist. Saving and reloading the game, or going back to Apocrypha and returning should fix this.
 * If the Dragonborn falls into the water it results in death. When the game reloads the autosave, their health will continuously go down, even though in Solstheim. Loading a previous save is the only known fix.
 * When you use the perks book to exit out of The Sallow Regent, your health bar continues to go down. On two accounts this was fixed by going back into the book, conjuring a sword, start fighting the lurker while taking damage from the black 'fuzziness' and then falling/jumping down. A message appears on top left of the screen saying 'you cannot fight'. When it autoloads you, your healthbar is returned to normal.
 * If the Dragonborn is stomped on by a Lurker  they can be flung into the air similar to a Giant. When they respawn in Solstheim they can end up unresponsive, walking into the ground or laying on their side. The only known fix is to load a previous save.
 * Upon entering or exiting Apocrypha, any spells, shouts, or powers equipped will be immediately unequipped.
 * The Dragonborn may be unable to leave apocrypha by reading a Black Book. To return to Solstheim, the Dragonborn can "die" by going into the water.
 * Sometimes there are two copies of Untold Legends. Attempting to re-enter Apocrypha by reading Untold Legends may not happen, thus permanently locking the player out of that part of Apocrypha. The only known fix is to reload a previous save.
 * Entering and Exiting Apocrypha with Dragon Aspects active may cause the Dragonborn's facial hair to become invisible.
 * Sometimes reading a Black Book will cause the player to enter into a non-stopping load screen.  Current "fixes" are to simply skip reading them until Bethesda releases a patch.
 * Dialogue asking Neloth if he's found anymore Black Books may still be available even after the Dragonborn has found all five. Neloth will point the Dragonborn towards a location that has already been cleared of the Black Book, thus rendering the quest impossible to complete.
 * Sneaking or dashing inside a moving tunnel causes Dragonborn to fall through the moving object abruptly and usually die due to the hazards below. (using Whirlwind Sprint can help you pass trough some of these tunels without falling)