Frozen Prison

Frozen Prison (氷結牢獄) is the maximum-security prison where the Great Tomb of Nazarick keeps its prisoners.

Background
The prison is managed by two Area Guardians: Nigredo and Neuronist Painkill. Nigredo was only the Area Guardian of the above-ground portion of the Frozen Prison while Neuronist was the Area Guardian of the underground portion was in charge of this facility located on the 5th Floor.

The Undead King Arc
According to Albedo, the commander of the Slane Theocracy's Sunlight Scripture captured by forces of Nazarick has been incarcerated in the Frozen Prison.

The Bloody Valkyrie Arc
Ainz Ooal Gown and Albedo paid a visit to Nigredo in the Frozen Prison. After briefly alerting the area's spawned creatures they went to Nigredo's room to request her to use her surveillance abilities on locating Shalltear Bloodfallen.

The Pleiades Day Arc
Due to her actions, Nigredo was confined in the Frozen Prison with Pestonya Shortcake Wanko as her cellmate. Later, with permission from Ainz, Yuri Alpha secured their release to assist her in building a Sorcerer Kingdom sponsored orphanage.

The Witch of the Falling Kingdom Arc
An hour after listening to the Floor Guardians' briefings on the war with the Re-Estize Kingdom, Ainz went to the Frozen Prison to have a meeting with Nigredo and Pestonya.

Layout & Features
The Frozen Prison resembles a fairy-tale castle but the interior is anything but magical. Various wraiths and undead lie in wait, hidden from seeing eyes to launch themselves at trespassers. Located in the fifth floor of Nazarick where the entire terrain is a frozen wasteland, escape from this stronghold is impossible.


 * Room of Nigredo: The cell where Nigredo, Overseer Guardian Albedo's sister, is kept in confinement. The entrance to her chamber is disguised as a painting of a mother cuddling her baby.
 * Room of Truth (Pain is not to tell): Neuronist Painkill's personal place of office. In other words, where Neuronist and her Torturers process freshly caught captives for interrogation. It's filled with a number of horrendous torture contraptions and equipment.
 * In Mass for the Dead, the function for Frozen Prison, save for Nigredo's cell, had to be shut down to conserve resources. Hence, Neuronist's torture facility was relocated to the floors under Shalltear Bloodfallen's control.

Trivia

 * It is said that the temperature inside the prison is even lower than that of the Arctic world of the 5th Floor.
 * Cocytus is known to be training in his home at the Frozen Prison, and was visited by Shalltear.
 * In Overlord: The Undead Oh!, the Frozen Prison resembles an icy mansion.