R'lyeh is a fictional underwater city created by writer H.P. Lovecraft in his stories about cosmic horror. It is famously known as the resting place of the ancient entity Cthulhu, who is said to lie in a death-like slumber beneath the waves. The city is described as having strange, non-Euclidean architecture, making it both fascinating and terrifying. In Lovecraft's mythos, R'lyeh rises from the ocean every few millennia, bringing chaos and madness to those who encounter it. The city symbolizes the unknown and the insignificance of humanity in the vast universe, themes that are central to Lovecraft's work.