One of the biggest additions to the game gets one of the smallest Re-Cuts. However, there are still some interesting things that have been hidden away in the files:

Dawnguard
Thaer and Rogen (unused NPCs) – carriage drivers cut from the quest which featured a crashed carriage and no drivers so, unfortunately for them they're part of that now.

Cave (unused location) – a small new cave, who would have guessed? It's inside the Soul Cairn. I finished off the location as it was missing some bits… such as a few walls…

Mistmen (unused NPC) – a slightly different and presumably earlier version of the Mistmen, only present in the new cave.

Dark Chasm (unused location) – another small new cave inside the Soul Cairn.

Map markers for Windhelm and Dawnstar docks (unused map marker) – actually already present in the game but disabled. Now they are enabled. The Riften one was actually also like these two before being enabled around the time of Anniversary Edition and these two just complete the set of every coastal city having one. The Windhelm one is a life changing convenience.

Various rings and amulets (unused items) – more vampire swag that can be found in Castle Volkihar, some of them even have vampire powers and are as follows: vampire amulets - Amulet of Bats, Amulet of Draining Grip, Amulet of Drain Magicka, vampire rings - Ring of Corpse Curse, Ring of Vampiric Grip, Ring of Draining Claws

Letter from Harkon, carried by Malkus (unused item) – game changing addition that places an unused note in Malkus' inventory.

Domna Magia, Jelkar, Vlokoslak (unused and cut NPCs) – vampire NPCs from the base game. All the NPCs were planned pre-Dawnguard and Domna Magia is actually even in base game Solitude but just disabled. Her outfit was changed by Dawnguard and as all three of them are in different places it just felt the most appropiate place to put them here. The other two can be found in Pinemoon Cave and Cronvangr Cave.

Empty wine bottles (unused items) – two variants based off of the more expensive wines. They are in Castle Dawnguard.

Silver food and drink platters (unused items) – quite self explanatory, platters with stuff on them. Also in Castle Dawnguard.

Part of the Re-Cut series - I will add links as they are uploaded:
Whiterun
Haafingar / Solitude
Hjaalmarch / Morthal
The Pale / Dawnstar
The Reach / Markarth
The Rift / Riften
Winterhold
Eastmarch / Windhelm
Falkreath | Granite Hill
Dawnguard (you are here)
Dragonborn / Solstheim
Miscellaneous
Anniversary Edition / Creation Club
Skyrim | Skyrim Legendary Edition

Q&A
Aren't there other mods that do this?
Yes, absolutely. There are plenty of good mods that do this already however none of them seemed to be as extensive as this one. I have literally added almost everything I could find that wasn't straight up broken or heavily reliant on a removed quest. Some parts have also been done a bit differently as there's almost nothing left of some parts so a little personal interpretation had to be used. This is also part of a series which is broken up into pieces so you can pick and choose which parts you may or may not want to keep, so if Whiterun conflicts with too much for you but you still like Hjaalmarch you can keep one and remove the other.

No quests?
Not at the moment, sorry. I think there's a reason a lot of the cut quests haven't been touched and that's because it's like trying to assemble a jigsaw in a foreign language with no instructions and plenty of pieces either being wrong or missing. That also includes almost anything to do with the Civil War. There are already some mods that do a lot of that and it would take an absolute Creation Kit master to be able to restore some of the stuff that hasn't been already.

You missed something and I am sad it's not here...
If you think that, then great. Not the sad bit but rather that if you found something I did not then please tell me about it and I'll see if I can implement it.

Isn't this all just removed cut content added back to the game? What do you mean by your tags of "cut, unused and created"?
Cut means you can find reference to it in the files or other sources like the strategy guide but wasn't literally present in the files. I tried my best to recreate it how Bethesda may have done but can't guarantee it's 100% how they would have done it. Unused means I basically just put it back in the game because it couldn't be found anywhere in the in-game world. Created means I added it in myself because it was just logical, such as an inkeeper to an unused inn or Thalmor in the Thalmor Headquarters. I have tried to restore everything as faithfully as I possibly could but some of it simply had next to nothing left to work with and required some of my own input.

Compatibility
This mod should work on pre-existing saves and be okay to install mid-game.

I actually made sure that it would work with a few other popular mods like all of the Creation Club content, the Unofficial Skyrim Patch, ESO / Legends Imports, Populated Skyrim and a few smaller scale ones like Khajiit Caravan Mules. Should be pretty compatible with most mods, aside from cut content mods like Cut Content Restoration that add to the Soul Cairn as the only two bigger edits are both there.