Carcosa is a fictional city in Ambrose Bierce’s short story “An Inhabitant of Carcosa” (1886). The ancient and mysterious city is barely described and is viewed only in hindsight (after its destruction) by a character who once lived there. Its name may be derived from the medieval city of Carcassonne in southern France, whose Latin name was “Carcaso.”
American writer Robert W. Chambers borrowed the name “Carcosa” for his stories, inspiring generations of authors to similarly use Carcosa in their own works.
Source: Carcosa – Wikipedia
Tim B.
“Lake Hali is a misty lake found near the city of Hastur. In the fictional play The King in Yellow (obliquely described by author Robert W. Chambers in the collection of short stories of the same title), the mysterious cities of Alar[1] and Carcosa stand beside the lake.”
Tim B.
https://en.wikipedia.org/wiki/Yellow_Sign
“The King in Yellow never fully describes the shape and purpose of the Yellow Sign. Nonetheless, “The Repairer of Reputations”, one of the stories in the collection, suggests that anyone who possesses, even by accident, a copy of the sign is susceptible to some form of insidious mind control, or possession, by the King in Yellow or one of his heirs. The stories also suggest that the original creator of the sign was not human and possibly came from a strange alternate dimension that contains an ominous and ancient city known as Carcosa. “
Tim B.
https://en.wikipedia.org/wiki/The_King_in_Yellow
“There are ten stories, the first four of which (“The Repairer of Reputations”, “The Mask”, “In the Court of the Dragon”, and “The Yellow Sign”) mention The King in Yellow, a forbidden play which induces despair or madness in those who read it.”