Narnia

 was a fictional location.

It featured in a series of books, including The Lion, the Witch and the Wardrobe. To get to Narnia, one had to go through a wardrobe. (PROSE: Cat's Cradle: Warhead)

Narnia was a land of lions, wicked witches and fauns. (PROSE: Enter Wildthyme)

It was cold. (PROSE: Escape Velocity, Anachrophobia, The Secret in Vault 13)

Sam compared the inside of the Doctor's TARDIS to Narnia. (COMIC: The Hyperion Empire)

When Jack Irvine found himself in a Sea Devil habitat, he compared the trip with going to Narnia. (COMIC: Clara Oswald and the School of Death)

Matteusz Andrzejewski had read the Narnia books and disliked the parts dealing with the character Susan Pevensie. (TV: Detained)

In non-valid sources
After entering a wardrobe, a young boy entered a forest in Narnia before encountering the White Witch. Upon noticing the boy, she made him disappear, with him reappearing near the Borrowers. (TV: )

Other matters
Narnia is a location from The Chronicles of Narnia book series, later reappearing in the BBC television series of the same name.