Related Article: OM TDS The Sunken Citadel.
Outer Sunken Citadel
The Sunken Citadel is an ancient ruin that can be entered from the underground drainage in the Docks area, sealed by a glyph. Inhabited by the Kurshok, a fish-like people, Keeper Rafe mentions, the place 'swarms with strange creatures'. Centuries ago, the Kurshok were a proud people that claimed dominion over the "aboveworld", and were favorites of the Trickster (also known as the Leafy Lord, and after the fall, the Leafy Devil). Bestowed with riches and power from the Trickster, they lived in peace until their rulers became arrogant and greedy. The Trickster banished the entire civilization to the underground, where, by the time Garrett arrived, they had lost the ability to read and considered the "aboveworld" to be a myth.
Throughout the ruins are numerous books from before and after the fall, describing the events and cataloging the line of kings until an unspecified period in the past (presumably when the Kurshok lost the ability to read and write).
The Citadel contained the Glyph Key needed to unlock the Compendium of Reproach which disappeared underground along with Keeper Rafe too long ago to remember. While stealing the Glyph Key, Garrett also steals the Kurshok Crown artifact from the Kurshok Crown room.
The Citadel is also inhabited by Pagan Rat Beasts which relentlessly battle the Kurshok Sword Guards at any opportunity. Garrett can use this to his advantage by firing Noisemaker Arrows to bring them together, where they will fight to the death.