Nacreum
The Nacreum is a transdimensional prison composed of intelligent nacre.
The Nacreum was built to hold slippery characters such as The Eel.
The Nacreum is (usually) located in Abalonia. Gnotilus, the founder and first citizen of Abalonia, keeps many of his prisoners in the Nacreum.
The Nacreum can travel quite widely in time and space. It does this independently of Abalonia, which has similar abilities. This time-space travelling ability is presumed (by whom?) to be some form of the Gnomon Algorithm.
Euphoriolanus occasionally gets himself committed to the Nacreum for what he he calls "a bit of recreational incarceration."
In the News
Nacreum designed to hold slippery characters such as The Eel.
Guards use Nacre sticks to enforce discipline within The Nacreum.
Socrates could have saved himself by accepting imprisonment in the Nacreum; but he preferred to die the Athenian way.