I'm wondering if datacentres have changed in the last 25+ years...
When I was going to a datacentre near Sterling, VA -- the building was unmarked, there was no visible 'front door' from the street. When I finally found it, the door was 4" thick, and took a substantial amount of effort to open.
Inside, you were in an empty room with no chairs, the security guards were behind bulletproof glass, and their office was about 3' higher than the floor in the room. There were multiple assault-style weapons displayed on the wall behind them.
You had to provide your name, company, and cage number before they slid down a steel box to put your driver's license and company ID into. They kept both until you returned to leave the building.
I was accompanied by an armed security guard.
The man-trap was a 25' long inclined hallway with 1" pipe spigots pointing down to the floor. When I asked what the pipes were for, he said "Urethane Foam" but didn't elaborate. To get through the door at the top of the man-trap it required a badge, an 8 digit number entered onto a PIN pad, and a biometric hand scan.
When I got to the company's cage, I was told "Don't leave your cage without calling downstairs first." Cell phones didn't work in the building, so they would hand you a wired telephone to plug in inside the cage. I wasn't about to disobey the guy with the gun.
Admittedly, this was the most extreme place I'd been, but I've also been to cold-war-era nuclear bunkers inside mountains of granite, and a small, unassuming building in the English countryside with no windows that I was told could withstand a plane hitting it -- because 90% of the building was underground.