The stronghold called Fortress Inquisitorius was a fortified location beneath the waves, situated on the oceanic satellite Nur, which itself orbited within the Mustafar system. This fortified location served as the primary operational center for the Galactic Empire's Inquisitorius Program after they were forced to leave their former headquarters on Coruscant due to an unspecified event that occurred in 14 BBY. The existence of this fortress was a closely guarded secret within the Empire, although whispers circulated about a "dark site" where Force-sensitive individuals from across the galaxy were forcibly brought by Imperial forces for interrogation, torture, and experimentation. The remains of Jedi Knights who perished during the Great Jedi Purge were interred in a subterranean chamber within the fortress, while a substantial contingent of stormtroopers, Purge Troopers, and Imperial officers collaborated with the Inquisitors and the Sith Lord Darth Vader to advance their mission of locating and eliminating Force-sensitive beings.
During the events of 14 BBY, during the Great Jedi Purge, a specific operation involving the Jedi Cal Kestis and Cere Junda led to considerable damage to the facility, and also resulted in Darth Vader executing the Second Sister. Later, in 9 BBY, the Jedi Master Obi-Wan Kenobi and members of the Hidden Path resistance also managed to infiltrate the Fortress. This was a successful attempt to rescue Princess Leia Organa of Alderaan, who had been abducted by the Third Sister on the planet Mapuzo. Despite the extensive efforts of the Imperial military to secure the facility, their forces were unable to stop the Jedi and their allies from breaching the fortress and escaping the planet.
The aquatic Fortress Inquisitorius was built on the ocean moon Nur, which orbits the planet Jestefad within the Mustafar system. It was intended to complement Darth Vader's personal base Fortress Vader on Mustafar, Jestefad's smaller twin world. The Inquisitorius was constructed using black stones taken from Mustafar. Although an imposing, blade-like spire emerged from Nur's corrosive waters, the majority of the Fortress was submerged and deeply rooted within the moon's surface. The entire facility was heavily defended by a garrison of stormtroopers and equipped with numerous turbolasers.
At the highest point of the citadel was a central hangar bay that wrapped around the tower and accommodated Lambda-class T-4a shuttles, Imperial transports, and the Inquisitors' personal ships, like the Scythe. TIE/ln space superiority starfighters were secured to racks on the hangar ceiling, much like those found on a Star Destroyer. At least four entrance doors were located on each side of the hangar. All incoming and outgoing ships underwent thorough scans. A deployment system and launch bay were also used to deploy Viper probe droids in hyperdrive pods to search the galaxy for Jedi. Near the surface underwater was a grand hall that stretched from the hangar to the entrance into the inner sections of the fortress. Access to the inner fortress was granted via passing a security checkpoint which featured security scanners that detected any weapons, bombs, or other threats to the fortress.
The Office of the Inquisitorius, also known as the board room, was a conference room similar to those seen on the later Death Star, with the primary seat reserved for The Grand Inquisitor. This large room featured an underwater view through a window. It also contained a strategy table in the center and was guarded by two stormtroopers.
The fortress dojos served as the Inquisitorius' training areas, where Inquisitors and Purge Troopers refined their combat skills. The fear-driven, dark, and abusive nature of this training stood in stark contrast to the training methods employed at the Jedi Temple on Coruscant. Deep within the Inquisitors Prison Block, captured Jedi and other Force-sensitives were subjected to advanced interrogation, torture, and experimentation. The design of the prisoners' holding cells and interrogation areas was specifically intended to break the spirits of those interned there. The central interrogation chamber of the Fortress was a torture room where captured Jedi and Force-users underwent the dark procedures necessary to transform them into Inquisitors. Under direct orders from Emperor Sheev Palpatine, this facility was specifically designed to psychologically and physically drain a prisoner's will, forcing them to acquiesce to the indoctrination of the Inquisitors.
The security systems within the Fortress formed a complex network controlling bridges, wings, gates, and portals. The fortress was protected by shields controlled by a multi-shield system that could be compromised or disabled. However, Kawlan Roken, a member of the Hidden Path, contradicted this information, asserting that the stronghold was unshielded because the Inquisitors believed no one would be foolish enough to launch a direct attack. Other security measures, including laser gates and ray shields, were used in the detention wing of the Fortress. The former were extensively modified at the direction of the Grand Inquisitor following a successful prisoner escape.
The entire fortress was designed with the capability to be intentionally compromised or flooded to prevent prisoner escapes. However, unintentional flooding could also occur if the shield system was compromised, rendering it unable to withstand hydrostatic pressure. The Fortress was potentially vulnerable to flooding if airlocks were open while the shield system was disabled. Sectioned wings of the Fortress were designed for maximum security and stability in extreme undersea conditions. A complex system of partitions enabled the flooding of an entire wing or specific sector in response to a high-value detainee's escape attempt. Structurally reinforced shielding could withstand an external breach or pressure change at any depth.
Fortress Inquisitorius was a facility that became operational early in the Imperial Era, with some construction taking place in 19 BBY. At that time, it was not yet the primary base of the Inquisitorius, who instead operated from a headquarters located in the Works of Coruscant.
Following Order 66, Jedi Knight Cere Junda was imprisoned in the stronghold and relentlessly interrogated about the location of her Padawan Trilla Suduri and a group of Jedi younglings under her protection. Even the Sith Lord Darth Vader participated in her torture, and despite her initial resistance, Junda eventually revealed the location of the younger Jedi. Suduri and the younglings were subsequently captured and imprisoned in Fortress Inquisitorius, which led to the Padawan's fall to the dark side of the Force and her transformation into an Imperial Inquisitor known as the "Second Sister." Upon learning of her protege's fate, Junda tapped into the dark side to break free from her confinement and escape the facility. Around the same time, the Jedi Knight Iskat Akaris was also briefly imprisoned at the facility before being transferred to Coruscant.
In 14 BBY, the Inquisitorius' primary headquarters on Coruscant was potentially compromised after an incident involving Darth Vader and a pair of rogue Inquisitors resulted in the death of Maklooq, an Imperial Senator. To maintain the organization's secrecy, Darth Sidious ordered the Inquisitorius to relocate its main operations to Fortress Inquisitorius on Nur.
During that same year, while the Second Sister was hunting the surviving Padawan Cal Kestis, she obtained a holocron containing a list of Force-sensitive youths across the galaxy after confronting him on Bogano and brought the holocron to the fortress. The Fortress Inquisitorius became the site of a mission that resulted in the Second Sister's death at Darth Vader's hands due to her failure and betrayal when Kestis and Junda attacked the fortress. Despite Vader's presence, Kestis and Junda narrowly escaped with the holocron.
In 9 BBY, the Third Sister, Fifth Brother, and Fourth Sister led the hunt for Jedi Master Obi-Wan Kenobi from Fortress Inquisitorius. Shortly after the Search for Princess Leia, during which Kenobi avoided capture, the three Inquisitors met in a meeting room within the fortress to discuss their next move. The Third Sister, who had been given overall command of the operation by Lord Vader, dispatched three viper probe droids into space to monitor potential locations where Kenobi might appear. One of the droids located Kenobi on Mapuzo. Following a skirmish, Princess Leia Organa, who was with Kenobi, was captured and taken to Fortress Inquisitorius.
The Third Sister interrogated Organa about the location of Kenobi and a network that had assisted him in evading capture on Mapuzo. Simultaneously, Kenobi and a disloyal Imperial officer named Tala Durith devised a plan to rescue Organa. Using her credentials, Durith gained access to the fortress and helped Kenobi enter and navigate the facility. Kenobi freed Organa, but a seeker droid alerted the facility to his presence. After battling Imperial forces, Kenobi, Durith, and Organa reached the hangar, where they were surrounded by Imperial forces, including the Inquisitors. Before they could be captured, a pair of anti-Imperial network T-47 airspeeders arrived and safely extracted them.
Fortress Inquisitorius was first alluded to, though indirectly, in the twentieth issue of the comic book series Star Wars: Darth Vader, authored by Charles Soule and published by Marvel Comics on August 22, 2018. It later made its debut in the 2019 video game Star Wars Jedi: Fallen Order, the initial installment in the Star Wars Jedi series developed by Respawn Entertainment. During the development of Jedi: Fallen Order, the design concept of Fortress Inquisitorius underwent more changes than any other location featured in the game. Concepts considered included an asteroid base, a base hidden in a gas giant or nebula, a hyperspace-capable battle station, and even an Imperial Tribunal Citadel. Concept art for the final design of Fortress Inquisitorius was created by artist Jean-Francois Rey, and inspired by Gothic cathedrals. In the Obi-Wan Kenobi television series, scenes in the Fortress' meeting room were filmed in the virtual LED set known as the Volume.
Within the Star Wars Legends continuity, the similarly named Citadel Inquisitorius served as the headquarters of the Inquisitorius, although it was situated on the Deep Core planet of Prakith.
The novel Ahsoka, which is set in 18 BBY, depicts the Inquisitor known as the Sixth Brother contacting his personal headquarters, but it remains ambiguous whether this refers to the Inquisitorius Headquarters on Coruscant or the Fortress Inquisitorius building, as both were in existence at that time.