This category of texts is centred upon entirely fictional realms with no correspondence of any direct kind to the real world within the text. We might think of such worlds as simply involving pure fantasy, but this category also includes science fiction as well as children's literature. This form of literature tends to only emerge from the late 19th century onwards. Because the world is entirely fictional it also often (though not always) contains a map of that world to ground the reader and make it seem as if it is a real place that can be mapped.
This spatial type also often involves a series of related texts with the same base setting and writers who are not just creating a located fictional place but an entire superstructure. So we have Tolkien's Middle-earth and Ursula Le Guin's archipelago world of Earthsea as well as entire planetary mapping in Frank Herbert's Dune. In terms of time and space/place then these worlds strongly signal that they are "other": entirely different from the known world and challenging all of our assumptions.
Lewis Carroll, Through the Looking Glass
J. R. R. Tolkein, The Hobbit
Frank Herbert, Dune
Ursula Le Guin, A Wizard of Earthsea
Mervyn Peake, Gormenghast