The Duke's Archives was granted to Seath along with his dukedom by Gwyn as a reward for his assistance in defeating the Everlasting Dragons.
Rhea of Thorolund may end up imprisoned here; possibly kidnapped by one of the Channelers and has Hollowed in a cell in the Archive Tower. The tower was once a trove of precious tomes and letters but became a prison after the onset of Seath's madness according to the Archive Tower Cell Key. The serpent men who guard the prison know not the value of what they hide. In the basement of the tower are the writhing "mistakes" (the Pisacas) of the terrifying experiments which were conducted there.
There are several Channelers in the Archives, sorcerers that serve Seath the Scaleless. Even after the onset of Seath's madness, they ventured far and wide to find their master suitable human specimens for his experiments.