Metafiction is self-conscious about language, literary form, storytelling, and directly or indirectly draw attention to their status as artefacts
(From Wikipedia's description of metafiction.)
I'd say Lord of the Rings fulfills this.
Self consciousness about language:
Tolkien was a philologist. His thing was constructing languages. To begin with, each ...
There is one part in particular in The Two Towers where Frodo and Sam are discussing the story as a narrative that strikes me as metafictional in a way different than other comments have mentioned:
“I don’t like anything here at all,” said Frodo, “Step or stone, breath or bone. Earth, air and water all seem accursed. But so our path is laid.”