decades ago I built these, here is one of my many files

Vast underground facilities, bigger than football stadiums - some buried more than two thousand feet below the surface, fully stocked with food, artificial underground farms, re-directed underground rivers, miles and miles of underground roads large enough for two tractor trailers traveling in opposite directions to pass each other with room to spare. These facilities have vast underground mass-transit systems connecting them to one another. The facilities are fully self-sufficient, generating their own electric, possessing air filtration systems, water purification systems, and vast supplies of guns and ammunition.

So gigantic are some of these facilities, that full sized U.S. Navy guided missile cruisers, destroyers and even nuclear submarines can approach secret ocean entry points, slide gently onto massive rails, and be gently transported over a hundred miles under dry land, through gigantic tunnels to half a mile underground, or coming to rest in water-filled underground "docks." The planning and sophistication of these government bases is almost unfathomable, but they exist. The government refers to these facilities as DUMBS Deep Underground Military Bases & Structures.