Fans of the HBO series True Detective (2014), which your humble narrator recently watched en bloc, have praised the show not only for its excellent acting and direction, but also for writer/creator Nic Pizzolotto's intelligent and subtle incorporation of themes from American occult fiction. On the surface, Season One of TD is a buddy-cop story, in which two deeply dysfunctional but ultimately simpatico detectives track the leaders of a murderous pagan cult. Just below the surface, the story crawls with references, some obvious and some veiled, to H.P. Lovecraft (1890-1937) and his works. One of the main characters, Rust Cohle, actually resembles author photos of Lovecraft: tall, gaunt, affectless, conservatively dressed, toting a ledger reminiscent of a musty old grimoire. In Episode 5, Cohle, in a double allusion to the extra-dimensional horrors of Lovecraftian fiction and to Edwin Abbott's Flatland, argues that extra-dimensional observers would perceive humans' lives as endlessly repetitive circles. The series as a whole takes place in Louisiana, one of the settings of HPL's seminal story “The Call of Cthulhu,” and its villains reek of rural degeneracy, incest, and insanity, themes in several of Lovecraft's stories. Those villains, the cultists, recognize Cohle's inner darkness and amplify his eerie trans-dimensional musings with their own references to a dark cosmos beyond this one (“black stars”) and, more notably, to “the Yellow King” and “Carcosa.”
These last two references are actually to characters and places Lovecraft borrowed from Robert Chambers' anthology The King in Yellow. Chambers's stories tell of an evil supernatural king, a haunted city, and a cursed play that unites them. (Chambers, in turn, borrowed names and ideas from Ambrose Bierce and Edgar Allen Poe.) More recent fantasy writers have used either Carcosa or the Yellow King in their works: Marion Zimmer Bradley, for instance, employed the place names “Carcosa,” “Hastur,” and “Hali” (all from Chambers's mythosphere) in her Darkover novels, while Lawrence Watt-Evans used the Yellow King as a major character in his under-appreciated Lords of Dus novels. The Lovecraftian Call of Cthulhu role-playing game had several adventures referring to these arcane entities.
True Detective, to the best of my knowledge, is the only television series to employ these references, and also the only one to show a version of Carcosa itself. Episode 8 portrays this mythical place as a maze-like jumble of rooms, cluttered with timbers and brambles and children's clothing, within an abandoned underground fort. My “read” on TD's Carcosa is that Pizzolotto intended it only to serve as an avatar or manifestation of the actual city, which according to Chambers and Lovecraft actually stands on another world, somewhere in the Hyades or near the star Aldebaran. The show itself remains silent on this matter, but it has kept all such otherworldly entities entirely off-screen. Cohle makes vague references to unseen pan-dimensional beings, the evil cultists make sacrifices to someone or something undefined, the Yellow King appears by name but never in the flesh*, and no actual monsters appear except for human beings who commit monstrous acts. (One of the most resonant scenes in the series, in Episode 3, has Cohle intoning "there's a monster at the end of it" right before viewers get their first look at cult leader Reggie Ledoux, half-naked and face hidden by a gas mask.) “Carcosa” is thus, I would suggest, an earthly place warped by spiritual or ideational proximity to the actual otherworldly city of madness**, just as the monstrous beings at the heart of True Detective's storyline are earthly humans warped by their devotion to supernatural or otherworldly beings. Whether these beings actually “exist” within the series's milieu, or are just figments of cultists' imaginations, is another question Pizzolotto leaves unanswered, and perhaps that's just as well. The worst horrors are usually the ones readers or viewers conjure up in their own minds, just as the most outre and fearsome demons are the ones that stare back at us out of the mirror.
* Jason Shankel of io9 has an alternate theory about the Yellow King, one which is consistent with other clues in the series but also takes away some TD's supernatural frisson.
** That proximity may be more than just spiritual: at the heart of the “Carcosa” maze, Cohle briefly glimpses a hovering, luminous, coelenterate structure that may in fact be a gate to another reality, or to the actual Carcosa.