R'lyeh
ruinThe nightmare corpse-city risen from the Pacific, where dead Cthulhu lies dreaming in his house. Johansen's crew made landfall on it in April 1925 at S. Latitude 47° 9', W. Longitude 126° 43'.

R'lyeh is the sunken citadel of the Great Old Ones, built in eons behind history by the shapes that came down from the dark stars, and the prison-tomb of great Cthulhu. When the stars came right in the spring of 1925 the city rose from the Pacific floor, and its emergence broadcast the dreams that drove sensitive men across the world to madness.
The crew of the captured yacht Alert, under second mate Gustaf Johansen, sighted its monolith-crowned citadel and went ashore. Its geometry was wrong by every earthly standard — surfaces convex and concave at once, angles behaving like other angles — and when the sailors pried open the great carved door, what lay dreaming inside came out. The city sank again beneath them; of the whole crew only Johansen survived to write it down.
To the cult's testimony gathered by Legrasse, R'lyeh was doctrine: the Great Old Ones all lay in stone houses in their great city, preserved by the spells of mighty Cthulhu; the great stone city with its monoliths and sepulchers had sunk beneath the waves, and the deep waters had cut off the spectral intercourse of thought — but the high priests said it would rise again when the stars were right. The vice-admiralty record knows the place only as an unknown island on which six of the Emma's crew died on March 23rd; Johansen's manuscript tells the rest — the landing at a sloping mud-bank on this monstrous Acropolis, the polarizing miasma through which the very sun of heaven seemed distorted, and the immense carved door with the squid-dragon bas-relief.
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Every fact above traces back to the text.
“Then, driven ahead by curiosity in their captured yacht under Johansen's command, the men sight a great stone pillar sticking out of the sea, and in S. Latitude 47° 9', W. Longitude 126° 43' come upon a coastline of mingled mud, ooze, and weedy Cyclopean masonry which can be nothing less than the tangible substance of earth's supreme terror”
The Call of Cthulhu (1928) — Chapter 3, The Madness from the Sea
“In his house at R'lyeh dead Cthulhu waits dreaming.”
The Call of Cthulhu (1928) — Chapter 2, The Tale of Inspector Legrasse — translation of the cult chant
“The great stone city R'lyeh, with its monoliths and sepulchers, had sunk beneath the waves; and the deep waters, full of the one primal mystery through which not even thought can pass, had cut off the spectral intercourse. But memory never died, and high priests said that the city would rise again when the stars were right.”
The Call of Cthulhu (1928) — Chapter 2, The Tale of Inspector Legrasse
“Johansen and his men landed at a sloping mud-bank on this monstrous Acropolis, and clambered slipperily up over titan oozy blocks which could have been no mortal staircase.”
The Call of Cthulhu (1928) — Chapter 3, The Madness from the Sea