It is located just east of Irkngthand. It is the location of Alain Dufont, whose death is an objective of the Dark Brotherhood quest "Mourning Never Comes." In addition, it is overrun by bandits, Falmer, and Dwarven Automatons. At the end of the dungeon, the Dragonborn may exit to Skyrim or Blackreach. If the Dawnguard DLC is installed, this is also the location of one of the Aetherium Shards for the quest "Lost to the Ages."
The first room inside the ruins contains a flame trap blocking the way forward, with a charred skeever impaled by a pole that is set up so the flames will cook it. Damage can be minimized using Whirlwind Sprint or Become Ethereal to go through it without getting burned, or it is possible to go around the back (right) side of the post that is shooting fire. Straight ahead is an expert-locked gate with Alain Dufont and two other bandits behind it. With high enough Sneak and Lockpicking skills, the gate lock can be picked and Alain killed without too much trouble.
The alternative is to proceed the long way around. At the flame trap, a hallway leads to the left. Down the hall is a large room with a single bandit towards the left (northeast) side. The right (southwest) end of the room contains two more bandits and a workbench. The path proceeds down a hall and to the right, where an open gate leads to the same room with Alain Dufont and two other bandits. Alternatively, straight ahead is a master-locked gate can be opened, and through it and to the right are two Dwarven crossbow mechanisms aimed at the bandits that can be used by pulling the levers next to each one.
After the bandits are dealt with, a gate underneath the crossbows leads to another large room with a bandit and many fallen rocks. The room contains more loot, mostly behind a locked gate. Through the next door and around a corner lies a Dwarven sphere and then another door. The next large room contains loud gears, a spider worker, and two more Dwarven spheres.
The next door should be open, and leads to a hallway with a Dwarven spider worker, and then stairs with a double blade trap, which should shut off automatically after the spider worker is defeated. Note that the blades tend to be very glitchy, so a save is recommended before going through the open door. If the blades don't stop after defeating the spider worker, they can be bypassed by getting next to the parts of the wall where they can't reach, then once the blades are past, running to another part of the wall to get to the top. Next is a pusher/flame trap, and two more Dwarven spheres. Up the stairs leads to a hallway with another workbench, a short set of stairs up, four spider workers, and, at the end, an elevator to the Raldbthar Deep Market.
Raldbthar Deep Market
Down the corridor is a ramp down with another spinning blade trap. At the end is a door leading to steps down to a large room with many Falmer and two skeevers in a pen. On the far side is a set of stairs that lead up to a spiral ramp up to a platform with more Falmer. Another ramp leads down again to a button that drops a draw bridge from back at the previous platform. Back up the ramp, the draw bridge can now be followed up to another platform and another ramp down. From here, the rooftops can be crossed to gain access to a room behind Dwarven metal grates. A hallway leads to a door, then to a set of steps down to a room with many pipes and escaping steam. Be careful of the floor trap at the top of the stairs, which triggers a ballista trap that can kill the player instantly. Within this room is a seemingly inaccessible chest on the floor above. There is a series of four large tubes slanting up and to the left. Using jump, the Dragonborn can climb up one of these slanted tubes. At the top, turn around and use Whirlwind Sprint to access a small ledge. Follow this ledge back toward the ballista trap location and you can access the chest. Another method is to trigger the nearby pressure plate trap with a bow then jump atop the bars as the trap resets, at the right angle to not slide off. Use the small broken stone just past the trap, furthermore you must move over to the other side of the bars to avoid getting pushed off by the pipes above that side. The back of the trap acts as one solid platform, despite appearing as individual bars.
The next room possesses a large quantity of Dwemer scrap metal, four buttons and a blocked hall to the left. The first button will activate a fire trap, the third button will open the gate, and the other two do nothing.
Through the door beyond the open gate is a room with a gate, a few leveled Falmer, and two chaurus behind another gate to the left (south) that is novice locked. The chauruses can be shot with arrows or destruction spells through the opening to the left of the gate. Since they cannot escape the area, they are good for practicing stealth by simply walking around them. If stealth is blown, walk into a yurt on the other side of the pool until they lose track and stealth is re-entered. There is a bridge with a button labeled "unpowered." To lower the bridge, you must clear the large gears around the room of bones that are stuck in there. Clear the right hand gear at the entrance to the bridge pointing on it (you will then see what is stuck in there) and remove it. Clear a second gear on the left hand side of the room past the Falmer hut. Clear a third gear on the right hand side of the room. The final gear is underwater between the two stairs - hard to see. After all four blockages have been removed, head up the stairs to where the bridge will drop and press the button located on a small plinth to the left hand side of the platform. After unjamming all the gears, the button on the bridge can be pressed, which drops a draw bridge and activates a Dwarven centurion, though at higher levels, it may be a centurion master.
Behind the centurion is a door that leads to a hallway with a lever at the other end that opens a gate. This room contains two Dwarven spiders and a Dwarven Mechanism, which opens a set of stairs down to a door that leads to Blackreach. If The Elder Scrolls V: Dawnguard is installed, the hallway to the right will contain an Aetherium Shard. The hallway to the left contains a lever which returns the player to Skyrim.
- 2920, vol 08 - Last Seed – Sneak skill book on a table in the room with Alain Dufont.
- Aegisbane – on Alain Dufont's corpse.
- Human Flesh – A rare alchemy ingredient located in the market in the first room with Falmer, by the skeever cage.
- Aetherium Shard – At the end if Dawnguard is installed.
- The various bones jamming the gears powering the bridge may spawn on the floor or near the gears, instead of wedged in them.
- The objects jamming the gears may not respond to the player. Backtracking to the area that the bandits were in and then returning may fix this.
In the market place of the under city, there's a spider robot running on the other side of the walls. It can't be seen but an enemy tag on the direction bar will be noticeable.
- Unjamming the gear underwater last may also fix this.
- If the player returns to the dungeon upon completion, the jammed gears may reset but the objects jamming them might not. This makes it impossible to access the end of this dungeon after reset. Installing the Dawnguard DLC will reset the dungeon for Lost to the Ages. The jammed gears should function normally after this.
- On PC or console the end of the dungeon may still be accessible if this occurs by using a wooden plate to glitch through the door to the elevator which leads to the deep market.
- On PC, it's possible to type tcl in the console to disable clipping and fly through the bridge. Until a bug fix is released this can at least be used as a workaround.
- A possible method for avoiding the aforementioned bug is to exit the dungeon from the front. Then complete Dark Brotherhood contract for Muiri by returning to her. Upon completion, the Dragonborn may now go north of Winterhold in search of Septimus Signus's Outpost.
- The boss, who would normally attack, may follow without attacking.
- Blackreach through the Raldbthar Dwarven elevator to Skyrim, the game may freeze (not fixed by patch). When trying to leave
- Sometimes upon entering the ruins after doing the Dark Brotherhood mission, it will not be possible to proceed deeper into the dungeon due to an invisible wall.
- When entering the water to un-jam the cogs the game might crash, save first.
- Sometimes, when unable to remove the items to power the button, exiting the area to the previous one and then returning does not fix the problem. It can glitch even more and cause the pieces to be immovable objects on the floor.
- When entering the left hand side of the pool, if one swims against the wall on the left and turn around, they will see a strange half-pillar which is only visible and solid from this side.