The Boeing factory in Everett, Washington, is the largest building in the world. Just north of Seattle, the 13,385,378 m3 building was constructed to build the first 747's in 1968, and is currently the place where the Boeing 747, 767, 777 and 787 are assembled. The factory employs over 30,000 people.
I visited last year and got a special flight back to Oslo on the maiden flight of the first 737 MAX to be delivered to Norwegian airlines (also pictured). It was pretty fun to see the CEO of Norwegian sprawled over three seats in the row in front of me, trying to get a bit of shut eye. There were no business class seats on that plane, but the champagne kept on coming.