Dooku's throne room, alternatively called Dooku's chambers, and also referred to as Dooku's great hall, or simply the great hall, was a prominent hall situated within the primary tower of Castle Serenno which was located on the planet of Serenno.
This immense chamber, characterized by its towering ceiling, featured the formal throne and desk of the Count. These were prominently positioned on an elevated dais at the room's far end. The throne's rear was adorned with a circular glass window, measuring 22-meters in height, and etched with the sigil representing House Serenno. Sunlight permeated the room through this window, casting a greenish illumination. Concealed behind the desk was a secret turbolift, providing transportation throughout Castle Serenno's main tower. A gangway directly connected the throne chamber to the Count's sleeping chamber.
Well before the Clone Wars commenced, Count Dooku pledged to Asajj Ventress that he would impart knowledge of the dark side of the Force to her, but first she needed to prove her worth.
In the year 20 BBY, Count Dooku made contact with Darth Sidious from within the hall, where he received the order to eliminate Ventress. Dooku followed his master's command. Subsequently, Ventress contacted Count Dooku in the same location during the Battle of Sullust, requesting his assistance, which he refused. Instead, he commanded a Recusant-class light destroyer to destroy the command ship, resulting in her crashing it into the main hangar. He then communicated with Sidious, falsely reporting Ventress's death, unaware that she had survived the battle.
Within the great hall, Dooku engaged in combat with individuals he believed to be three Jedi, who were in reality Nightsister assassins wielding lightsabers: Ventress, Karis. Dooku emerged victorious and expelled the three attackers from the castle, resulting in the shattering of the hall's window.
Later, Mother Talzin contacted Dooku, informing him that she might have a replacement for a Sith assassin, given Ventress's presumed demise. Dooku expressed interest in Mother Talzin's proposition and journeyed to the planet Dathomir to meet with her. Subsequently, he encountered Savage Opress, who had undergone magically enhanced by the Nightsisters, and accepted him as his apprentice.
Subsequently, Dooku provided lightsaber combat instruction to Opress within the great hall.