Cidhna Mine is a prison in Markarth.
It is run by the Silver-Blood Family who use prisoners to mine the silver ore inside.
Skyrim -- No One Escapes Cidhna Mine w/ Alternate Endings
It is also home to Madanach, the King in Rags and leader of the Forsworn Rebellion. It is commonly referred to as the most secure prison in Skyrim.
The Forsworn Conspiracy, No One Escapes Cidhna MineEdit
Margret, an undercover operative of the Imperial Legion, was sent to Markarth by General Tullius to retrieve the deed to the mine.
The Legion feared the Forsworn and the Silver-Bloods were Stormcloak sympathizers, who wanted to exploit the violent criminals imprisoned in the mine and use them against the Empire.
While investigating the Forsworn Conspiracy at the request of Eltrys, the Dragonborn is either imprisoned here; framed for murdering several notable members of the Silver-Blood family; or infiltrates the mine intentionally, hoping to meet Madanach and disable Forsworn influence over Markarth.
If the Dragonborn returns to Markarth after they have completed the quests that occur at Cidhna Mine and have a bounty, choosing the "go to jail" option will transport them to Cidhna Mine.
To leave the mine, activate one of the ore veins using a pickaxe, triggering an option to serve jail time.
Finding a shiv, wielding a pickaxe, or using a spell to attack any of the inhabitants of the mine provokes everyone nearby to relentlessly strike back at the Dragonborn, with many using magic.
Sneaking or Invisibility effects allow for picking off the inhabitants more easily as the Dragonborn's lack of armor, accessories, and strong weapons leaves them vulnerable to multiple attacks.
Another alternative solution is if the Dragonborn is either a Werewolf or a Vampire Lord, they are able to transform in the mine which is useful for escaping, general combat or killing Madanach if needed.
- Five silver ore veins.
During "No One Escapes Cidhna Mine," the veins do not produce ore, regardless of how long they are mined, and unlike other veins, the animation proceeds forever.