So all those hundreds (if not thousands) of contract employees all have never mentioned it?!?!
Their families who ask Husband/Dad, “What did you do at work today?” “Just another day building a secret underground city for the rich in case there’s a nuclear war, honey.”
Yeah, I believe it exists. /sarc off/
Actually, hiding something that big can be done, and it has been done. I worked on a defense project in the 1990’s that had been hidden in plain sight since the late ‘80’s. Workers were told that they could not even tell their wives where they worked. The work sites were spread across the world, thousands of people were involved.
An investigation was launched after rumors started circulating, and it was found that they were coming from the military.
Of course, that was during the Cold War, and it was viewed as a vital defense project.
I think it would be hard to sell to civilians that what is essentialy a luxury housing project is a vital secret.