|“||[T]he nightmare corpse-city of R'lyeh [...] was built in measureless eons behind history by the vast, loathsome shapes that seeped down from the dark stars. There lay great Cthulhu and his hordes, hidden in green slimy vaults [...] until the end.||„|
|~ HPL, "The Call of Cthulhu"|
R'lyeh (pronounced /ˈɹu.li.a/ or /ɹɪl.ˈai.ɛ/) is a fictional island city created by H. P. Lovecraft, which makes its first appearance in the 1928 short story "The Call of Cthulhu". R'lyeh is also referred to in Lovecraft's "The Mound" as Relex.
R'lyeh is a sunken city located deep under the Pacific Ocean and is where the Great Old One Cthulhu is interred. R'lyeh's bizarre architecture is characterized by its non-Euclidean geometry.
When R'lyeh rises in Lovecraft's short story "The Call of Cthulhu", the only portion of the city that emerges is a single "hideous monolith-crowned citadel" in which Cthulhu is entombed. The human onlookers are awed by the sheer immensity of the city and by the frightening suggestiveness of the gargantuan statues and bas-reliefs.
The city is a panorama of "vast angles and stone surfaces [...] too great to belong to anything right and proper for this earth, and impious with horrible images and disturbing hieroglyphs." The geometry of R'lyeh is "abnormal, non-Euclidean, and loathsomely redolent of spheres and dimensions apart from ours." The strange architecture of the city makes navigation on foot disorienting and treacherous; surfaces that appear flat may actually be tilted, and angles of masonry that appear convex at first glance may actually be concave.
In Lovecraft's stories, R'lyeh is sometimes referred to in the ritualistic phrase "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn", which roughly translates to "In his house at R'lyeh, dead Cthulhu waits dreaming."
Lovecraft said that R'lyeh is located at 47°9'S 126°43'W in the southern Pacific Ocean (HPL: "The Call of Cthulhu", The Dunwich Horror and Others). August Derleth, however, placed R'lyeh at 49°51'S 128°34'W in his own writings (AWD: "The Black Island", Quest for Cthulhu the great). Both locations are close to the Pacific oceanic pole of inaccessibility (48°52.6'S 123°23.6'W), the point in the ocean farthest from any land. Derleth's coordinates place the city approximately 5100 nautical miles (5900 statute miles or 9500 kilometers), or about ten days journey for a fast ship, from the real island of Pohnpei (Ponape). Ponape also plays a part in the Cthulhu Mythos as the place where the "Ponape Scripture", a text describing Cthulhu, was found.
One source suggests that R'lyeh in the Baltic sea, describing Cthulhu as being "scraped from a nest in the drowned wreckage of a city on the Baltic floor." (EXP: A Colder War [Charles Stross]). It has also been said to be found off the coast of California (EXP: Move Under Ground [Nick Mamatas]).