The Duke's Archives is a massive library in Dark Souls, located atop the highest peak in Anor Londo and accessible after the player has placed the Lordvessel at Firelink Altar. It lies within the duchy of Seath the Scaleless, a dragon who was granted the title of Duke by Lord Gwyn for his service during the war against his own kind, the Everlasting Stone Dragons, at the dawn of the Age of Fire. The Archives is a legendary storehouse of arcane knowledge amassed by Seath in an effort to achieve immortality through magic, primarily based on experiments involving Crystal Sorceries. Seath's research eventually led him to his goal of eternal life by way of the Primordial Crystal, but not before being driven to madness by his obsession. As a result, the Archives have fallen into disrepair, and the subjects of Seath's twisted crystalline experiments now roam through its corridors.
A large clocktower at one end of the Archives has been converted into a prison for Seath's test subjects; freshly-captured specimens are typically kept in one of the cells here until they can be used for experimentation. The prison is guarded by serpent-men who will raise an alarm during any escape attempt, which also releases several Pisaca enemies from the lowest cell. These nightmarish abominations are feared even by the serpent-men guards and will seek out the player with slithering efficiency. Big Hat Logan may also be encountered in this area once he is freed from a cage in Sen's Fortress. After being rescued again from a large cell inside the Archives prison, Logan relocates to the main library to study and begins selling new Crystal-based Sorceries to players with sufficient Intelligence.
The majority of the Archives' texts are housed in two cavernous multi-story chambers covered in bookshelves. This area is patrolled by several Undead Crystal Soldiers and three powerful Channelers who serve as Seath's elite guard. A few outdoor balconies offer a magnificent view of Anor Londo as well as the gnarled mass of crystal that protrudes up from nearby Crystal Cave.
The Duke's Archives is riddled with elaborate mechanisms; elevators and rotating staircases operated by levers provide access between the upper floors of the Archives, and secret passages can be opened to reveal hidden chambers and shortcuts in certain locations. After traversing the majority of the Archives, players can activate a set of collapsible stairs leading out of the library and into a wooded area filled with Crystal Golems, as well as the entrance to Crystal Cave. Sieglinde of Catarina may also appear in this area if the player has followed Siegmeyer's optional quest-line up through his departure for Blighttown. She is trapped inside a Golden Crystal Golem that must be killed in order to free her.