Water Cavern

"The water from here supplies the whole town."

- Gaius to Merlin

The Water Cavern is an expansive cavern system beneath the Citadel of Camelot. It contains the city's water supply and is accessible through a single locked door in an outer wall of the castle.

History
Soon after Merlin arrived in Camelot, Nimueh magically transported an Afanc into the water cavern to poison Camelot's water supply. Though the deaths were initially blamed on a magical plague, after Merlin and Gaius discovered that the pathogen was spread through water, they went to the well to investigate and found the Afanc. Merlin later returned to the cavern with Arthur and Morgana to kill the creature (The Mark of Nimueh).

When Arthur killed a Unicorn, he triggered a curse that turned Camelot's water supply to sand (The Labyrinth of Gedref).

Trivia

 * It is unknown if the cavern is connected to the Dragon's Cave or the Burial Vault, which are also located beneath the citadel (The Dragon's Call, Excalibur).