This entry may be the slightest bit convoluted.
I discovered (wasn't hard) that Carcosa as a physical place was filmed at Fort Macomb in New Orleans East. Here's the Wikipedia page on it.
Yet Carcosa is also a thing one believes in, as Miss Delores told us in episode 7:
"You know Carcosa?" she asks Cohle."What is it?""Him who eats Time. His robes is a wind of invisible voices...Rejoice. Death is not the end. Rejoice! Death is not the end! You know Carcosa! Rejoice! Carcosa!"
Carcosa is a male figure worshiped through his triumph over time itself, a point easy enough to sell to Christians if there are other motivating factors, such as access to or gaining of political power. This moves us away from both Bierce, who mentions Carcosa in his short-short story "An Inhabitant of Carcosa." Bierce's narrator wakes up in a world between worlds, anxious to return to his family in his beloved city of Carcosa. Bierce also mentions Carcosa in "Haita the Shepherd," but in that story, Carcosa is a god. In these ways, True Detective parallels Bierce's usage of the term, as well as Chambers's use, given that Chambers refers to it as a place.
The inner ring:
Carcosa is a place that twists reality. As Cohle, then Hart behind him work their way through the concentric circles of Carcosa, lured on by Childress's words echoing in the tunnels, we see devil nets, skeletons, skulls, rags of clothing, and other items hanging from the driftwood that shapes a tunnel within the brick-and-mortar walls of the abandoned fort. Here, Carcosa is a place that destroys artists as it lures others in.
Childress has shaped his vision of Carcosa as a cloister or temple, with a concentric arrangement. This reverberates within many works of detective fiction, especially Umberto Eco's The Name of the Rose, where the monastery under investigation has a library that is a series of concentric rooms and levels; in this library is where the key crimes have taken place and where the murderer offers his confession as he poisons himself with the pages of his own weapon. In True Detective, the concentric maze of Carcosa becomes a method of both concealment and revelation. Childress uses his voice to both guide and disorient Cohle, calling him a "little priest" to entice him on even as he waits to attack. The phrase "little priest" evokes the priestly role of the investigator, even as Cohle wanders through what is essentially Childress's central atelier. At the center is the throne room, yellow skeletons forming the throne and a circular opening in the top of the dome. (Here, Cohle has yet another hallucination, and it's one that reverberates with any Call of Cthulhu character: It's an open gate. I fairly cheered when I saw it.) Fittingly, it is here in the center of Carcosa that the battle with Childress begins and ends.
Because Carcosa is a physical place, it's linked to south Louisiana. Carcosa is a palimpsest, possibly the primary text on the metaphorical vellum of this narrative. Given that we do not learn when the cult began--we know it's been around at least since relatively early forms of black-and-white photography, and Courir de Mardi Gras itself dates back to rural medieval France. As a religious locus, Carcosa is linked to Catholicism, given that Catholic practices in south Louisiana (significantly more present than Protestant) are the norm. Catholicism overlays the cult activity, rendering the cult activity more difficult to see.
I have a separate idea map for the notion of the palimpsest, so I will leave that for later.
Carcosa as mythology is a bit more difficult to resolve. Should the "proof" of a religion depend on evidence of a deity's work? If so, no religion measures up beyond individual belief. It's clear that Miss Delores believes in Carcosa, and it's clear that other cult members believe strongly enough to kill themselves (Reverend Tuttle) and others (even down to Officer Childress, who likely, though it's unproven, tells Guy Francis to kill himself in his jail cell). But what constitutes belief?
What constitutes the teleology of True Detective? Note what book the former Reverend Theriot sees in the Tuttle library: Telios de Lorca. I believe that the de Lorca part is not what's important; it's the Telios part, pointing to telos 'end, purpose, goal' and teleology 'study of purposiveness; study of objects regarding their aims, purposes, or intentions'.
Teleological language may be the detective's blind spot, a matter that I'll get into in another post.
Finally, does Carcosa indicate cargo-cult science? Does it represent a distant pole from scientific integrity? Cohle is able to find his way through Carcosa--although he certainly did not anticipate its location or form--by keeping his mind rational. We already suspect that Hart would not have reopened the case, possibly even if he'd heard himself from Guy Francis that the killer hadn't been caught. This kind of 'ratiocination' is what detectives have used all the way back to Edgar Allan Poe. Does Carcosa ultimately point to the cargo-cult nature of much of human activity?