Wikipedia
R'lyeh is characterized by bizarre architecture likened to non-Euclidean geometry. Norwegian sailor Gustaf Johansen, the narrator of one of the tales in the short story, describes the accidental discovery of the city: "a coast-line of mingled mud, ooze, and weedy Cyclopean masonry which can be nothing less than the tangible substance of earth's supreme terror—the nightmare corpse-city of R'lyeh...loathsomely redolent of spheres and dimensions apart from ours". The short story also asserts the premise that while currently trapped in R'lyeh, Cthulhu will eventually return, with worshipers often repeating the phrase Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn: "In his house at R'lyeh, dead Cthulhu waits dreaming".
Lovecraft claims R'lyeh is located at in the southern Pacific Ocean. Writer August Derleth, a contemporary correspondent of Lovecraft and co-creator of the Cthulhu Mythos, placed R'lyeh at . The latter coordinates place the city approximately from the actual island of Pohnpei (Ponape), the location of the fictional " Ponape Scripture". Both locations are close to the Pacific pole of inaccessibility , a point in the ocean farthest from any land mass.
In Brian Lumley's Primal Land short story "The House of Cthulhu", the island is referred to as "Arlyeh".
Charles Stross's novella A Colder War implicitly locates 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".
The Tsuburaya Productions tokusatsu series Ultraman Tiga places R'lyeh in the South Pacific, and the series' antagonist, Gatanozoa (who is an alternate version of Cthulhu's son, Ghatanothoa), was born there.