Terebinthia

Terebinthia is a sovereign island-kingdom in the Great Eastern Ocean, the closest island to it being the island of Galma, which is a duchy under the authority of the Kingdom of Narnia. In Voyage of The Dawn Treader, Caspian X claims that a sickness was going around and prevented them from landing

=Trivia= In Bridge to Terabithia the main characters create an imaginary world named Terabithia, the name Terabithia is likely derived from the name of this island. Though, Paterson herself has said the reference was not intentional.