Short answer: the U.S. government has a LOT of large, underground facilities — that's documented and not really in dispute. Whether any of them are hidden "cities" in the way conspiracy theories describe them is a different question, and the honest answer is: the evidence for true cities doesn't hold up.
What is verifiably real (declassified and on the record):
- Mount Weather Emergency Operations Center, Virginia — a Cold War-era continuity-of-government bunker carved into the Blue Ridge Mountains. Declassified in the 1990s.
- Raven Rock Mountain Complex ("Site R"), Pennsylvania — another major Cold War continuity bunker, near Camp David.
- Cheyenne Mountain Complex, Colorado — home to NORAD, the famous blast doors, hardened command center.
- The Greenbrier Bunker, West Virginia — a congressional relocation facility built under the Greenbrier Resort, exposed by a Washington Post story in 1992.
- Hundreds of decommissioned ICBM silos across the Great Plains, plus active missile fields.
- Tunnels under the Pentagon, the White House, Camp David, and other government sites for evacuation and secure communications.
These are large, hardened, expensive installations — often called "underground cities" in casual speech — built to keep government functioning after a nuclear strike.
What is speculation or conspiracy theory, not proven:
- A full "Dulce Base" — a claimed massive underground human/animal hybrid facility in New Mexico. No credible documentation. Repeated "exposed" claims trace back to a handful of fringe figures.
- Denver International Airport as a masonic/lizard-people bunker complex. The conspiracies ignore that a major chunk of the underground area is just baggage handling, and no evidence supports the rest.
- "City-sized" installations with tens of thousands of permanent residents under major cities. No verified location, no credible witnesses, no documentation.
The logical gap: modern tunneling costs run into the billions per mile for large-diameter tunnels, and delivering food, water, air, and power to a hidden population of thousands would require infrastructure any inspector or satellite could spot. A small classified command center is plausible. A hidden metro area is not.
If you're curious, a good place to start is declassified Cold War continuity-of-government history — the real story of places like Mount Weather and Site R is genuinely interesting and well-documented. What part are you most curious about?