The Dream Cycle is a series of short stories and novellas by author H. P. Lovecraft (1890–1937). Written between 1918 and 1932, they are about the "Dreamlands", a vast alternate dimension that can only be entered via dreams.
The Dreamlands are divided into four regions:
Other locales include the Underworld, a subterranean region underneath the Dreamlands inhabited by various monsters; the Moon, accessible via a ship and inhabited by toad-like "moon-beasts" allied with Nyarlathotep; and Kadath, a huge castle atop a mountain and the domain of the "Great Ones", the gods of Earth's Dreamland.
Evidently all dreamers see the Dreamlands slightly differently, as Atal, High Priest of Ulthar, mentions that everyone has their own dreamland. In the same sentence he says the Dreamlands that many know is a "general land of vision".