> Governments around the world already keep many locations/facilities secret and hidden from the public.

Those cold war bunkers only had one purpose: to keep high ranking government and military peeps alive just long enough (up to 2 weeks or so) to make sure that mutual destruction is actually 'assured'. They were not meant as some sort of cradle of a new civilization or as a safe haven to survive a nuclear war (because there would be no place to return to anyway).