De-frosting a building-sized refrigerator

The Fulton Market Cold Storage Company building in Chicago has been, well, storing cold things since the 1920s. But last July, the company sold the building and moved to a more modern facility outside town, leaving the old cold storage warehouse to be turned into offices.
But first, the new owners had to defrost it.

Video

The Fulton Market Cold Storage building has ice-covered walls for the same reason a freezer can get covered in hard, packed ice. When you put something into a freezer — say, a giant slab of beef fresh from a slaughterhouse — that thing contains moisture. There's liquid trapped inside it. Over time, especially if it's not sealed very well, that moisture will turn into water vapor in the air. When temperature changes cause that vapor to condense back into liquid, it instantly freezes — turning to ice anywhere it touches.
In your fridge at home, that's just an annoyance. At the Fulton Market Cold Storage building, it was epic.
Besides the video linked above, you should really check out the amazing photos taken for the ice, pre-melt, by photographer Gary Jensen.