Castle Serenno, alternatively referred to as Dooku's palace or Dooku's fortress, was situated on the planet of Serenno. It functioned as the residence of Count Dooku, who was both a Sith Lord and a leader within the Separatist movement. Moreover, it served as the central hub for House Serenno. Protection for the palace was provided by battle droids.
The location of Castle Serenno was upon the planet of Serenno, standing alone at the edge of a significant cliff. Three meticulously designed ornamental gardens enhanced the palace, each positioned at the front of the palace. Visitors would traverse a lengthy pathway nestled between these gardens to reach the palace's front. Here, they would encounter the primary tower, soaring to a height of 120 meters, where Count Dooku typically managed his affairs. Surrounding the main tower were ten relay buildings. The main tower itself boasted a 22-meter-high stained glass window offering a panoramic view of a sprawling city in the valley below. Additional buildings and defensive outposts were integrated into the cliff face. A double row of obelisks stood before the palace's main entrance. By the time the Clone Wars erupted, the palace and its surrounding estate were defended by numerous legions of Separatist battle droids.
The interior of the palace reflected Dooku's sophisticated preferences. The corridors were lavishly decorated with the finest furnishings. Art from across the galaxy adorned the walls, while statues from bygone eras stood silently. However, the opulent displays for visiting dignitaries concealed cells and torture chambers situated deep within the cliff face, where Dooku conducted interrogations and executions. During the war, Castle Serenno not only served as the headquarters for House Serenno but also functioned as a stronghold for a prominent figure within the Separatist movement.
Dooku's birth occurred around 102 BBY. Upon discovering that his second son, Dooku, possessed force-sensitive abilities, Count Gora contacted the Jedi Order. He then abandoned the young Dooku in a forest near the palace, a location known to be inhabited by spine-wolves.
In 42 BBY, Count Ramil acquired the services of Abyssin mercenaries who had been hired by the Great Houses of Serenno to protect against pirates. He then instructed them to invade Serenno and its capital city, Carannia. As the Abyssins seized control of Serenno, Ramil remained in the palace with his droid army. He later departed to force the insurgents fighting the mercenaries to surrender, aiming to restructure Serenno by eliminating all the Great Houses and falsely accusing Dooku of murdering his sister, Jenza. However, this plan failed, and Ramil was killed by Dooku. Dooku then declared himself the new Count. After some persuasion, the Great Houses concurred and requested a summit. Following discussions about the summit's location, given the destruction of Carannia during the invasion, Dooku proposed holding it at Castle Serenno. The Great Houses agreed, and the summit took place at Castle Serenno.
Around 23 BBY, LEP-10019 escorted Ventress from the palace balcony to the palace's great hall, where Dooku was present. Ventress then encountered Dooku, who interrogated and tortured her with Force lightning for lying about her intentions to assassinate him. He subsequently ordered her to locate Jenza, Dooku's sister. However, Ventress questioned this order, prompting Dooku to torture her again with Force lightning. Dooku then threw Data disks onto a table in front of Ventress, instructing her to begin her search in the Trannon district of the capital city, Carannia. Ventress complied and departed to fulfill the mission, after Dooku warned her of the consequences of failure. After completing her mission, with Dooku intervening to save her by eliminating the Republic agents attempting to take Jenza offworld, Ventress experienced a vision in the palace's great hall. She saw Dooku at a table covered with papers and data slates, an unusual sight for the count. Urged by the ghost of Jedi Master Ky Narec, she approached Dooku and overheard him lamenting why no one else could follow his commands. Ky Narec's ghost then questioned Ventress about her allegiance to Dooku. Before Ventress could respond, another figure resembling the Dooku she knew emerged and verbally criticized Ky Narec's ghost for being a disappointment and a failure. Unable to bear Dooku's criticism of her former master, Ventress fled to a forest near Castle Serenno, overwhelmed by whispers of Ky Narec and Dooku, before being transported in her vision to the Outer Rim planet Rattatak.
Early in the Clone Wars, an incident on the Colonies planet Cato Neimoidia resulted in the deaths of at least 3200 civilians. In response, Count Dooku broadcasted from his home, condemning the Republic and asserting Separatist innocence. At the end of his broadcast, he challenged the Galactic Republic to send Supreme Chancellor Sheev Palpatine to Cato Neimoidia to exonerate the Republic.
In 20 BBY, former Sith assassin Asajj Ventress and two other Nightsisters launched an assassination attempt on Count Dooku, seeking vengeance for her former master's betrayal of her. Arriving on Serenno aboard a GS-100 salvage ship, the three Dathomirians infiltrated Dooku's palace. They struck him with a poison dart in his bedroom to impair his vision, forcing him into a lightsaber duel throughout the castle. Despite their efforts, Ventress and her fellow Nightsisters failed, as Dooku struck them all with his Force lightning and hurled them through the main tower window. Mother Talzin then brought Savage Opress to the palace to become Dooku's new apprentice. Dooku instructed Savage that his anger was a source of strength that he needed to nurture to succeed. He subsequently dispatched him on a mission to Toydaria to capture King Katuunko.
Later, the mastermind Moralo Eval constructed the Box, a structure designed to assess a group of bounty hunters to form a team for kidnapping Supreme Chancellor Palpatine, within the palace grounds.
Subsequently, Dooku summoned General Grievous to Serenno and instructed him to slaughter Ventress and the Nightsisters on Dathomir. Mother Talzin attempted to assassinate Dooku while he was in his base, causing him significant pain. However, he contacted Grievous via comlink and ordered him to kill Talzin, directing the general to follow the green mist to locate her. Grievous rescued Dooku at the last moment. Believing that the Nightsisters had been destroyed, he shifted his focus to his former apprentice Opress, who had betrayed him at Talzin's instigation. He summoned Grievous to his base and informed him that he could sense Opress growing stronger daily. Although Grievous dismissed the idea that his former apprentice posed a threat, Dooku asserted that he was a threat to everyone, including them, and that something sinister was emerging.
Following Dooku's death at the hands of Jedi Knight Anakin Skywalker during the Battle of Coruscant and the subsequent end of the Clone Wars after Order 66 and the Proclamation of the New Order, the castle was abandoned. Sometime before 19 BBY, the nearby city was destroyed by an orbital bombardment carried out by the Galactic Empire. The Empire then dispatched a task force to seize the castle and extract Dooku's war chest. This task force, consisting of over forty clone stormtrooper under the command of Captain "Wilco," cleared the palace of all valuables and loaded them onto three class four container transports for removal from the planet.
Clone Force 99, a unit that had become rogue after the war and turned into mercenaries, disrupted the operation. They had been tasked by the information broker Ciddarin Scaleback to steal as much as possible. They successfully infiltrated the extraction site, but three members—Tech, Echo, and Omega—became trapped inside Transport Three when Wilco ordered its premature departure after spotting Force 99's leader, Hunter, lurking nearby. The infiltration team attempted to escape the vessel via the escape pods, but the ship's crew ejected them to strand the thieves on the ship. To return to the planet, the team boarded a container and detached it from the ship, using its emergency re-entry thrusters as a landing pod. Meanwhile, Hunter and Wrecker were engaged by Wilco's men and forced to retreat into the palace basement through a concealed turbolift. Although the squad managed to escape the palace grounds, the detached containers spilled their contents on Serenno's surface, resulting in the loss of approximately 15% of the chest's treasure.
This location was first seen in "Nightsisters", the twelfth episode of Star Wars: The Clone Wars' third season, which was broadcast on January 7, 2011. Jackson Sze created concept art of the exterior of Castle Serenno's main tower and relay towers for "The Box" episode in the fourth season of Star Wars: The Clone Wars. Jackson Sze also created the painting of Castle Serenno at night for the episode. Molly Denmark developed the lighting concept for the palace used in the Star Wars: The Bad Batch season 2 episode "Spoils of War".