The Citadel Inquisitorius served as the primary base of operations for the majority of the Inquisitorius. It was situated on Prakith, a planet characterized by its mountainous terrain and found within the Deep Core. This location was where the High Inquisitors were given their tasks and where Inquisitors held discussions with one another. The citadel itself was a formidable, somber tower that projected an ominous presence from its mountainous perch. The interior design shared characteristics with religious buildings found galaxywide, including high, arched ceilings and imposing obsidian pillars. Furthermore, it housed several detention cells and torture rooms utilized for questioning the most stubborn and hazardous prisoners.
Numerous inhabitants of Prakith asserted that the cries of Jedi undergoing torture within the citadel reverberated throughout the mountains for extended days.
Around 17 BBY, Denia, a Jedi Master, was captured by Valin Draco, her previous Padawan who had become an Imperial Inquisitor. She was imprisoned and subjected to torture within the depths of the Citadel Inquisitorius on Prakith. Subsequently, her comrades from the Alderaanian Resistance launched an assault on the Citadel in an attempt to rescue her. However, during the conflict, she gave her own life to ensure the Rebels could flee.