Are there any examples of runways that are under the cover of some terrain such as a runway built into the side of a mountain as a tunnel, perhaps with an entrance and an exit on both sides to facilitate go-arounds?
I could see advantages to this for national security purposes because of the natural protection from kinetic and explosive attacks provided by rock.
For example, I've spoken with Mormons who boasted that the Granite Mountain Records Vault could take a direct hit from a nuclear weapon and still remain intact.
I consider it a truism that any surface-based airport would be obliterated by a nuke.
I recognize that such a facility may not be declassified, but barring that, if they don't currently exist to public knowledge, is this something that would be reasonably possible to build?