Deephold

The Deephold is an enormous prison in the underdark, run by the drow of Umbravall. Prisoners of the Deephold have a single eye remove and replaced with a magical device called a Black Eye which allows Nightwardens to track them with their insignias. If the Black Eye is removed after being implanted, the prisoner dies within several months to a year. As such the device prohibits normal teleportation magic to different planes, as it will remain behind on the Material Plane. 
It is rumored that some parts of Deephold extend into the Abyss - a great deal of the prisoners are driven insane by the proximity. 
== Known former or present Deephold prisoners ==
Daggerspine, an Ancient Red Dragon.
Andrith Shadowbane, Vahlka's younger sister.
Amber Vaillow, a Lich.
Kosith, a Rakshasa.
Baurogh, a Beholder.