If you have been exploring the Morrow Parish Sanatorium in Remnant 2, you will have found a lady trapped in the basement. The former doctor in charge of the institute, her staff turned on her and locked her up, but you can free her. You will need to find the Prison Cell Key to free her. And you really will want to release her, as it leads to some great loot.
Getting the Prison Cell Key
The exact location of the Prison Cell Key in the Morrow Parish Sanatorium is on the third-floor balcony. Getting there is a bit of a chore, however. From the World Stone just outside the asylum, climb the ladder and head in the window. Make your way down the corridor and into the room with all the patients. Take out the nurses, then move through the open door on the far side of the room.
You will come to a large staircase, and you can head down, taking out some more nurses. Behind the table is a door that leads to the left, down into the basement. Take this, then when you arrive at the bottom, take a right at the giant spiderweb.
Go all the way to the end of the corridor, up and out the stairs to the side of the building. At the far end of the garden area, you will see a shack. Inside you will need to fight a boss called Ripsaw, and when the fight is done, you can grab the Third Floor Key.
Now, go back inside via the main doors, which you will be able to open from this side. Go back up to where you entered the building and then climb the stairs to the locked door. Use the Third Floor key to unlock the door. Take out all the Fae that spawn in and go into the room on the left. Take out more Fae, then jump out the window onto the balcony. Here, you will find the Prison Cell key that you can then use to free the lady in the basement. You will also find a Simulacrum, so enjoy the extra charge on your Relic that will unlock for you.
Now that you have the Prison Cell key make sure you have all three Stone-Carved Dolls before you go there. They will allow you to get your hands on the Dreamcatcher, a powerful melee weapon. That will then allow you to get the secret Invader class.