How to unlock: Speak with Ghostly Woman in Fifth Eye Tavern, in Cliff's Edge (M10.3).
In the right corner of Fifth Eye Tavern located in Cliff's Edge district (M10.3) you can meet Ghostly Woman. Speak with her and ask her who she is. The ghost attacks you but let her... strangle you. After you wake up in a mysterious place, speak with the ghost again. Ghostly Woman gives a quest in which you must find her "copies". Use the portals twice to leave the Labirynth and return to the city.
The copies can be accessed in any order. This quest doesn't require you to find all of them but this is not difficult to do. Below, you can find locations of all of the copies.
The first copy is Seria. If you want to meet with her you must complete another side quest - The Sorrow's Pray.
Loss-of-Self is the second copy and you can find her north of the tavern in Cliff's Edge (M6.1). Speak with her and tell her that she reminds you of a woman from the tavern.
The third copy is a girl called Avina. You can find her standing with other orphans south of the tavern in Cliff's Edge (M6.1). Speak with Avina and tell her that she is similar to a woman from the tavern. Ask her about the details and you can learn that Avina is also haunted by the ghost.
The last, fourth copy is Sigyn, the captain of levies. You can find her near the closed Council Tower in Government Square (M5.1). Like with previous women, speak about her familiar look.
When you find all of the copies you must return to the Labyrinth. You can do this by, for example, ordering a dangerous drink in the tavern or meet with Idylla in Caravanserai and ask her to put you in a trance. Return to the location where Ghostly Woman is.
All of the copies that you have found, will appear in the Labyrinth. You should be especially interested in the ghost of Seria. When you get closer to her, a scene of the siege will be recreated.
Ghostly Man will also appear in the Labyrinth. Interact with him. The situation can be solved in two ways:
- Asking him how to stop the machine can irritate the ghost, causing him to summon Tabaht guards. You can fight alone or summon ghosts of your party members to help you (a much better choice). When the battle starts, attack only the guards. The ghost is invulnerable to your attacks.
- You can offer your help and then use Persuasion to change the ghost's mind.
Regardless of your choice, you get the information on how to turn of the Probability Engine. Speak with Ghostly Woman and leave the Labyrinth by using the portals.
Now, you must go to Buried Crossroads (M11). If you don't know how to access it you can, for example, check the guide chapter for The Cold, Calculating Jack main story quest. When you arrive there, you find the same engine as the one in your mind (M11.9). Approach it and try to disable it. You must use a skill connected with Intellect (Concentration or Tidal affinity) if you want to complete the quest. When you do this, you receive 40 XP.