Dooku's prison was a prison complex, comprised of numerous cells and torture facilities, that was carved into the rockface beneath Castle Serenno. The castle was perched high on a cliff on the planet Serenno, located in the Outer Rim Territories. A massive metal door, guarded by control panels in a lengthy palace hallway, served as one known entry point to the prison. One of the cells contained a force field.
In 19 BBY, Jedi Master Quinlan Vos was incarcerated within this prison, where he underwent torture at the hands of Count Dooku and various droids. [Asajj Ventress](/article/asajj_ventress], formerly a Sith assassin, and Boba Fett's syndicate later mounted a rescue attempt to free Vos; however, by that time, Vos had completely succumbed to the dark side of the Force and rejected their aid.
During the Clone Wars, [Asajj Ventress](/article/asajj_ventress], then a Sith assassin, participated in the questioning of various inmates held in the prison beneath Castle Serenno. Ventress later commented that no prisoners ever left the prison. Near the end of the Clone Wars, Jedi Master Quinlan Vos was captured and imprisoned by Count Dooku in one of the many cells under the palace, following an unsuccessful assassinate attempt on Dooku on the Outer Rim world of Raxus Secundus by Vos and Ventress. During his imprisonment, Vos was subjected to constant torture by droids, who also monitored his sleep schedule and provided meals erratically. Dooku would occasionally visit Vos's cell to watch the torture or unleash force lightning upon him, relishing his screams. Vos consistently tried to provoke Dooku into conversation, hoping he would reveal something, but according to Vos, this tactic proved unsuccessful. On one occasion, Dooku interrogated Vos, mockingly questioning him about his mission. Despite Vos's truthful answers, Dooku still instructed the torture droid to continue its work.
Ventress and Boba Fett's syndicate subsequently launched a rescue operation to free Vos. The bounty hunters created a diversion to distract the battle droids guarding Castle Serenno, while Ventress infiltrated the palace. While infiltrating the palace, Ventress engaged and destroyed numerous droids that were patrolling the interior. She eventually gained access to the prison, where she encountered Vos. However, Vos, enraged that Ventress had deceived him about who killed Jedi Master Tholme after using his psychometric abilities when holding Tholme's lightsaber, force-choked her. Vos then battled Ventress, despite her repeated pleas for him to resist fully embracing the Dark side of the Force. This forced Ventress and the bounty hunters to abandon the prison and the palace.
The prison made its debut in Christie Golden's 2015 canon novel, Dark Disciple. The location was later referenced in the Star Wars: Build the Millennium Falcon 70 Magazine.