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)