What sunken city is Cthulhu said to inhabit?

The sunken city where Cthulhu is said to inhabit is R’lyeh.

R’lyeh is a fictional city in the South Pacific introduced in Lovecraft’s short story “The Call of Cthulhu,” first published in Weird Tales in 1928. In the story, the city rises temporarily above the ocean, allowing a ship’s crew to encounter its vast, bizarre masonry.

Cthulhu is described as imprisoned or sleeping there, waiting for the stars to become right so that he can return. The city’s architecture is famously non-Euclidean: surfaces, angles, and distances behave in ways that defy ordinary human geometry. This makes R’lyeh more than a conventional lost city; it is a setting where reality itself becomes hostile and unreliable.

Sarnath and Ulthar are other fictional locations in Lovecraft’s stories, while Carcosa belongs chiefly to Ambrose Bierce and Robert W. Chambers. None is Cthulhu’s underwater prison. The name is often written with an apostrophe as “R’lyeh,” though typography can vary.