Raldbthar

Raldbthar is a Dwarven ruin, and is a more complex dungeon than most. The first level is infested by bandits, led by Alain Dufont, whose death is an objective of the Dark Brotherhood quest, Mourning Never Comes. The Raldbthar Deep Market is occupied by Falmer, which are apparently led by a Falmer Gloomlurker. Players will also encounter mechanical enemies, and at higher levels they can be rather difficult to defeat.

Walkthrough
Before the final boss you will come to a bridge with a button labeled "unpowered". You must go to the stuck gears in the room and remove various bones jamming the cogs to power the bridge. Note that one set of stuck gears is located under the bridge underwater. After you unjam all the gears, press the button on the bridge and you will activate a Dwarven Centurion.

The "boss" of the dungeon attacks immediately after the player solves the final puzzle. Using a bow and keeping your distance is advised. Once the boss gets within range, it will release a steam attack that can very quickly kill the player. However, it is possible to trick the boss to fall off the bridge and it will die in the water.

At the end of Raldbthar there is a Dwarven Mechanism which you lack the necessary item to activate. (First Dark Brotherhood Contract Area For Muiri). The item is an attunement sphere found in other dwemer ruins. To unlock the mechanism you need to travel north of Winterhold. Carefully walk down the mountain, or jump off the bridge path to the college and pray you land in the water (not suggested) then swim north past Skytemple Ruins, to a cave called Septimus Signus's Outpost. Once you have talked to Septimus he will give you a quest called Discerning the Transmundane and give you key to open the Dwarven Mechanisms. Raldbthar connects to Blackreach (by going through the Mechanism) which is part of the Discerning the Transmundane quest, so if you dont want to explore the location Septumus suggests or if you already went through that gigantic location and dont want to retun yet, then you can ignore the mechanism.

Bugs
 * The various bones jamming the gears powering the bridge may spawn on the floor or nearby the gears, instead of on them.
 * 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.