The Cerenerian Sea is a fictional place in H. P. Lovecraft's Dream Cycle stories. It is mentioned in Lovecraft's short story "Celephaïs" and his novella The Dream-Quest of Unknown Kadath.
The Cerenerian Sea is a great, sky-blue ocean in the Dreamlands. It connects many important places, such as Celephaïs in Ooth-Nargai, the port of Hlanith, the city of Inganok, the Nameless Rock, and the ruins of ancient Sarkomand.
By steering a ship toward the horizon, where the Cerenerian Sea touches the clouds, it is possible to sail into the sky; and thus reach places like the cloud-kingdom of Serannian.
References
Cerenerian Sea Wikipedia(Text) CC BY-SA