There was a period where I regularly got to go inside Boeing’s Everett factory for work (I didn’t work for Boeing though). For those who don’t know, it’s one of the largest buildings in the world, built in the 60s to manufacture 747s. Now they build all kinds of aircraft there.

“Big” is an understatement. Even “cavernous” falls short. It’s easy for your brain to forget you’re in an indoor space until you look up and see a roof over your head. It’s like a miniature city in there. It’s got its own road network, fire department, cafeterias, and I heard it can even have its own weather.

My route to and from the job site every day took me through alleyways and around sites where workers were actively putting airplanes together. I got to watch an entire fuselage be moved from one side of the factory to the other by the overhead cranes. But my favorite part of the whole place were the underground tunnels that you could use to get around. You could still see old civil defense fallout shelter signs in the stairwells, and even though I wasn’t supposed to take pictures in the facility I did anyway: