Original: While the particulars of their relationship with Cthulhu are unknown, it is clear that they arrived on Earth with him, where they constructed the city of R 'lyeh.
Simplified: In one of Lovecraft's tales, The Call of Cthulhu, he said that Cthulhu currently lies in a dreamlike state in the sunken city of R 'lyeh (rill-ee-yeh), waiting for the time when the Old Ones shall rise again. R' lyeh is located in the Pacific Ocean (though it is not a real city).