Ghyll:Agarttha
Mythical status aside, the temple city Agarttha has a physical existence in the Jorvyll mountain region. Outsiders know very little about either the history or exact location of its fabled bronze towers. This is not due to its perilous site among treacherous mountain passes or even the impenetrable concatenation of it's priesthood's morbid initiation rite, but rather those same cleric's complete, maniacal xenophobia.
This facet of Agarttha's society is has a long-standing precedent in its national religious text, "The Codex of The_Beast." The most poetic and eloquent example is translated here:
Whether seeker, pilgrim, or cenobite come hence
by western chance or questing from the east
whether man or god come 'fore these walls
We shoot 'em. Dead. Long live The *#@!ing Beast!
As may be guessed, the priesthood of Agarttha worships a deity known as The Beast. Rumors of cannibalism, necromancy, and poor dental hygiene are all true, which stands as a deterrent to the inquisitive. The city's secrets are safe even from the most debased Occultologists, and Ghyll scholars and the world at large should rest easy that only the tamest revelations will be parcelled out to the Encyclopedia.
Long live The Beast!