The Dreamlands is a vast, alternate dimension that can be entered through dreams, similar to astral projection. Experienced dreamers are among the most powerful inhabitants of the Dreamlands and may become its permanent residents after their physical deaths.
To reach the Dreamlands, a sleeper must find an unusual stairway in a conventional dream and walk down the Seventy Steps of Light Slumber to face the judgment of powerful gatekeepers named Nasht and Kaman-Tha. If judged worthy (i.e., able to survive the dangers of the Dreamlands), the dreamer is allowed to descend the Seven Hundred Steps of Deeper Slumber and emerges in the Enchanted Wood. When a person enters the Dreamlands in this way, he leaves his physical body safely in the waking world. Should he be killed during his travels, his corporeal body will only suffer a shock. Sometimes, however, this can be fatal; "dream death" of this kind makes return to the Dreamlands impossible.
Waking up causes a person's "dream self" to disappear, and the individual may have difficulty recalling anything learned or experienced during his time asleep (similar to conventional dreaming). The Dreamlands can be entered in other ways, including physically. This usually requires passing through very dangerous areas of both the waking world and the Dreamlands. Consequently, "real" death becomes a risk. However, the visitor does receive the prolonged lifespan of a native of the Dreamlands, and the traveler's time there is no longer limited to the duration of a night's sleep on earth.
Though the term "Dreamlands" typically refers to the dimension accessible by human dreamers, other inhabited planets apparently have their own dreamlands. Reaching these other realms from the terrestrial Dreamlands is possible, but difficult. Time flows at a different rate in the Dreamlands; each hour on earth represents a week or more there. Consequently, a traveler can spend months in the Dreamlands during a single night's sleep on earth. Fortunately for dreamers, inhabitants of the Dreamlands are either long-lived or immortal, provided they avoid injury or disease.
Despite its accelerated time, the Dreamlands rarely experiences change. Its geography, politics, and population remain fairly static. Dreamers, however, can exert great change over the topography, such as by creating entire cities with accompanying populations. The Dreamlands has its own pantheon known as the Great Ones, but they resemble powerful immortals rather than true gods because ordinary humans can wound, deceive, and seduce them.
Their dominion is protected, however, from mortal challengers by the dread Other Gods and their messenger Nyarlathotep (who treats the Other Gods and the Great Ones alike with evident contempt). Otherwise, the rest of the deities of the mythos, who figure prominently in Lovecraft's other writings (such as the Great Old Ones and the Outer Gods), have little interest in or influence over the Dreamlands.