In the Ruined King, you’ll come across a cell in the southwestern corner of the Anguish Cells in Thresh’s Dungeon at the Shadow Isles. To unlock the door, you’ll have to have the amulet plus 2 upgrades.
Once inside, approach the glowing red artifact and select the following options:
- Continue
- Submit to the vision
- Continue
- Take the keyring
- Escape the prison to the surface floor
- Reach for the blasting wand
- Continue
- Continue
As a reward for successfully making it through the nightmare, you’ll receive a Ritual Pendant of Power!