Paracosm

A paracosm is a detailed imaginary world created inside one's mind. This fantasy world may involve humans, animals, and things that exist in reality; or it may also contain entities that are entirely imaginary, alien, and otherwordly. Commonly having its own geography, history, and language, the experience of such a paracosm is often developed during childhood and continues over a long period of time: months or even years.

Examples of Paracosm include:

• K.C. Remington has written over twenty books in the Webbster and Button Children's Stories series, set in a paracosm called the Big Green Woods.
• Middle Earth, the highly detailed fantasy world created by J. R. R. Tolkien, as expressed in his novels The Lord of the Rings and The Hobbit, as well as a sizable body of writings published posthumously containing fictional histories, languages and other reference material. Tolkien had been inventing languages since his teen years, only later imagining the people who spoke them or their environment.
• Gondal, Angria, and Gaaldine, the fantasy kingdoms created and written about in childhood by Emily, Anne, and Charlotte Brontë, and their brother Branwell, and maintained well into adulthood.
• Hartley Coleridge, created and maintained the land of Ejuxria all his life.
• Austin Tappan Wright's Islandia began as a childhood paracosm.
• M.A.R. Barker began developing Tekumel at age ten.
• Borovnia, the fantasy kingdom created by Juliet Hulme and Pauline Parker in their mid-teens, as portrayed in the film Heavenly Creatures.
• The modern fantasy author Steph Swainston's world of the Fourlands is another example of an early childhood paracosm.
• Henry Darger began writing about the Realms of the Unreal in his late teens and continued to write and illustrate it for decades.
• Joanne Greenberg created a paracosm called Iria as a young girl, and described it to Frieda Fromm-Reichmann while hospitalized at Chestnut Lodge. Fromm-Reichmann wrote about it in an article for the American Journal of Psychiatry; Greenberg wrote about it as the Kingdom of Yr in her novel I Never Promised You a Rose Garden.
• As children, novelist C. S. Lewis and his brother Warren together created a paracosm called Boxen which was in turn a combination of their respective private paracosms Animal-Land and India. Lewis later drew upon Animal-Land to create the fantasy land of Narnia, which he wrote about in The Chronicles of Narnia.