- Main article: Keeper Library
- In the acolyte chambers there is a button on the ground that reveals the secret entrance to the forbidden library. The glyph upgrade is necessary in order to use this entrance.
- A button in Caduca's bookshelf opens the door to a secret room containing a book about the last glyph and some loot.
- The books contained in the forbidden library contain canonical information on diverse matters.
- Also in the forbidden library there is a biography of Garrett that summarizes the events that occurred in Thief 1 and 2.
- Map Inconsistency: The Keeper Library entrance is aligned with the Stonemarket gateway, but Orland's balcony is located on the west side of the library, contrary to in-game and cutscenes.
- All of the giant statues are holding books that Garrett can pick up.
- A candle on Orland's desk and another in the secret room are impossible to pinch out.
- When Garrett takes out a weapon or draws an arrow, the item will appear briefly floating in the centre of the main rotunda.