The Imperial Archives was a museum on Coruscant. It held a small cantina and Palpatine's vault with a mysterious Sith holocron inside.
The vault was perhaps the most heavily guarded room in the museum. Imperial Force Adepts as well as Royal Guards and elite Stormtrooper squads all guarded the room.
Other rooms in the museum held scale models of different planets, like Felucia, Tatooine, and Naboo. There was a room filled with scale models of Imperial armed forces, like dark troopers, AT-ATs, and even a model of the second Death Star. Many of these models could, when faced with threat, activate and fire at enemies. This happened to Silri when all three phases of Dark Troopers activated as she came near.
The holocron on the altar.
Tyber Zann and his forces attacked from three different directions to attempt to steal the emperor's passkey: Zann started just outside the Cantina, Urai Fen started in the Museum ducts, and Silri started at the center of the museum. Zann and his forces were able to fight through the different defenses in the museum, including the dark trooper models. Although skilled, the Force Adepts were also bested by Zann's forces, and he stole the artifact.
The archives were tended to by librarians which helped categorize materials. One of the librarians that worked in the archives after the Battle of Yavin was a Rebel spy that went by the codename, "Tigress." She was eventually found out, tortured and then executed by the Empire.
The Imperial Archives were briefly mentioned in the role-playing scenario, Death-Hunter. This same term was used to describe the museum encountered in Star Wars: Empire at War: Forces of Corruption. It is possible that this museum is one and the same with the Galactic Museum. Other sources suggest that Palpatine's private collections were housed in the Imperial Palace in Palpatine's Vaults. Since this museum does not seem to be a part of the Palace, it may be a different location, though it is difficult to understand why the Sith Lord would have housed his Holocron outside the Palace.