A: "It’s for loading in equipment. The bottom of the door is likeky flush with the floor of the room. It’s pretty common to see this on central office buildings as they are full of bulky/heavy equipment that is periodically updated. As you roam the city, if you look at these buildings you’ll often see several such doors, sometimes larger, and often several stories off the ground. It’s much more efficient to crane this stuff into the buildings fully/partially assembled than to move an enormous number of individual components and assemble them onsite."