Connects all of Skyrim's dwarven ruins to Blackreach, plus a few bonus features. The doors are placed such that they don't break any quests or give early access to dungeons. 

Click here for the Skyrim Special Edition version.

Here's a guide to where all the doors are in Blackreach: 
Looking at the door to Raldbthar Deep Market, there is a wall to the right with several doors: 
The door on the far left leads to Irkngthand. Initially it goes to the Grand Sanctuary, but if the relevant Thieves' Guild quest has been completed that room is flooded, so the door moves to the end of the Slave Pens instead. Also fixes a bug where the door connecting these two areas doesn't properly disable. 
The remaining four doors lead to Mzulft, Kagrenzel, Avanchnzel, and the Aetherium Forge underneath the ruins of Bthalft. 

Looking at the entrance to Tower of Mzark, there are some stairs down to the left leading to a small stone jetty by the water. On it are three doors, leading to Arkngthamz, Bthardamz, and Nchuand-Zel underneath Understone Keep in Markarth. 

Looking at the entrance to Alftand Cathedral, there is a door in the shadows to the right which leads to the Temple of Xrib under Sightless Pit. If you look further to the right and jump over the side, you'll see a lift mechanism. Activating it will take you to a small room with three doors, leading to the three Dwemer ruins of Solstheim. 



And here's where the doors are in the ruins themselves:

• Alftand - Use the mechanism right at the end of the level in the vanilla gane. 
• Arkngthamz - In the final room with the Aetherium Shard. 
• Avanchnzel - On the right wall, immediately before the final lift. 
• Bthalft - When you enter the final room with the Aetherium Forge, take the path to the left. 
• Bthardamz - On the left wall, immediately before the final lift. 
• Fahlbtharz - When you first reach the large room with moving platforms, the door is underneath the bridge section immediately in front of you. 
• Irkngthand - See earlier description. 
• Kagrenzel - When you reach the bottom of the pit, look for the tunnel leading out. The door is on the right. 
• Kagrumez - Look to the right when you enter the main area. 
• Mzark - The Tower of Mzark is accesed through Blackreach in the vanilla game. 
• Mzinchaleft - Use the mechanism right at the end of the level in the vanilla game. 
• Mzulft - In the final room, halfway up the observatory. 
• Nchardak - Starting from the coast, continue until you reach the main door leading inside but don't enter it, and instead go to the left and follow the ramp up to the roof, where you can activate a lift mechanism. 
• Nchuand-Zel - In the central area, at the very bottom of the central tower. 
• Raldbthar - The mechanism right at the end of the level in the vanilla game. 
• Xrib - The Temple of Xrib lies at the bottom of Sightless Pit. The door is behind the final lift. 
  

Bonus features:

• Near the door to Mzinchaleft Gatehouse, there is a portal to the wayshrine in Darkfall Cave. This will only activate if the location has been visited during the relevant Dawnguard quest. 
• If you follow the path up the mountain towards Kagrenzel, there is a hunter camp on the right. I have added a flight of stairs and a door which leads to Skuldafn. This will only activate if enough progress has been made in the main questline. The portal leading to Sovngarde should only be active if you have not yet reached Sovngarde in the main questline; this is to prevent you getting stuck in Sovngarde. 
• The Shrine of Azura and Sacellum of Boethiah both now have small shrines which give their blessing, identical to the ones in the temple in Raven Rock. 
• It is now possible to return to Japhet's Folly after completing the side quest "Rise in the East" by simply fast travelling there. The map marker is at the extreme North-East corner of the map. Alternatively, go to Windhelm docks, walk onto the deck of the ship furthest upstream, then open the trapdoor on the left. To return to Skyrim, find the ship some distance North of the island. There will be a ladder to take you back up to the deck, and a small door which leads to Windhelm. Note: You may encounter a bug where the bombardment of the island repeats. This is a problem with Skyrim, not this mod. I recommend using USLEEP.
  

Known bug - Followers can sometimes get lost, particularly when entering Skuldafn. They shouldn't take long to catch up though. 

Compatibility: 

• Small chance of conflict with mods which alter the quests "The World-Eater's Eyrie" and "Sovngarde" in the main questline, "Blindsighted" in the Thieves' Guild questline, or the side quest "Rise in the East" 
• Mods which significantly change the layout of Dwemer Ruins may leave doors in odd places but should otherwise be compatible. 
• Compatible with the Unofficial Skyrim Patch, even though this also fixes a bug in Irkgnthand.