Paracosm

Gondal is a paracosm.

Source: tatoeba (9099104)

Imaginary playmates and paracosms may chiefly represent the vast creative potential of inherently talented people, but in less elaborated forms, they may also represent what childhood imagination can offer to the growing person. Humanity has already benefited from the paracosmic visions of Plato, Thomas More, Aldous Huxley, Thomas Hobbes, Arthur Tappan Wright^([sic – meaning Austin Tappan Wright]) (Islandia), and J. R. R. Tolkien.

Source: wiktionary

Occasionally the fantasies of older childhood go well beyond the invention of a pretend friend. In fact, some children, typically at about 9 or 10 years of age, create "paracosms"—entire societies or worlds for the imaginary people to inhabit. [...] How common is it for children to create such elaborate fantasies, and what does the invention of a paracosm say about its creator?

Source: wiktionary

As Emily [Brontë] turned in on herself for resources, she created a new paracosm, the Kingdom of Gondal, which she shared with Anne [Brontë]. The paracosm of Gondal became a way of life for the sisters; they shared its secrets for the rest of their lives.

Source: wiktionary