Carcosa is an extraterrestrial city located next to the foggy Hali Lake and the city of Alar. In turn, these places are located on a planet of the Hyades, near Aldebaran. Black stars rise in its firmament in what appears to be a binary solar system.
The city of Carcosa has its origin in the story An inhabitant of Carcosa by Ambrose Bierce, published on December 25, 1886 in the San Francisco Newsletter. In turn, the writer Robert William Chambers took the name of Carcosa for his compilation of short stories "The King of Yellow". In some of which there is talk of a play that bears the same name. In this play you see more loans from "A Dweller of Carcosa" and other plays by Ambrose Bierce, such as "Haîta the Shepherd", naming Hali and Hastur (more as a place than as an entity). So was the way he came to Lovecraft, using these concepts in his work The Whisperer in Darkness.
The Yellow Sign is believed to have been created in Carcosa in the works of August Derleth, being Hastur's abode, and frequently confusing dimensions with Earth, dragging humans into this act. According to the writer James Blish, this is so because Hastur created Carcosa as a place for his exile, not being able to reign in Aldebaran.
Flora and faunaEdit
After the ruin of Carcosa, the Byakhees made their nests in the city. Tentative creatures, similar to cephalopods, live in nearby lake areas and mainly in Lake Hali.
In the Pathfinder universe, Carcosa is a highly magical planet which contains a living city that is also called Carcosa. It's the home of Hastur, who resides in the monstrous Lake of Hali. When the light from Carcosa's star shines on another world's night sky, Hastur's power increases on that world. Carcosa is continusly expanding, absorbing the societies and cities of other worlds. Serving as the fuel for Hastur's eventual ascenscion into the ranks of the Outer Gods. At which time he will consume and absorb Carcosa and its inhabitants. The city of Carcosa is a vast patchwork of the cities which it absorbed over the eons, each individual patchwork is a nexus, which may retain some of the properties of their original worlds. Some of the known nexues include Neruzavin (flying polyp city), Bohlvari (shoggoth inhabited elder thing city), a technologically advanced city of skyscrapers (inhabited by robots and aliens), and an underwater city (inhabited by the undead).