The Arcanum was a space station that was commissioned by the Sith Emperor for the purpose of holding dangerous Sith artifacts possessed by the reconstituted Sith Empire.
In 3638 BBY, amidst the Galactic War between the Empire and the Republic the rogue Sith Lord Tagriss raided the facility and stole the ancient artifact the Darkstaff and the Seeds of Rage on behalf of the Dread Masters. Darth Acina was set to defend it by the hand of the emperor.
Interior view of the Arcanum.