The sunken city R'lyeh

Deep beneath the surface of the Pacific Ocean lies a sunken corpse-city. Built eons before recorded history, R'lyeh is the prison of the sleeping Cthulhu.

The discovery of this place was described by the protagonist of one of Lovecraft's stories, Norwegian sailor Gustaf Johansen: “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 nightmare corpse-city of R'lyeh... loathsomely redolent of spheres and dimensions apart from ours.”

Furthermore, the city's architecture makes exploration and escape impossible. The structures are colossal and seem to be likened to non-Euclidean geometry - a system that deals with curved spaces rather than flat ones. In R'lyeh, changes in perspective can be observed, causing uncertainty as to what is vertical and what is horizontal.