TL;DR from Atlas Obscura:
One of the largest free-standing structures ever built, this dirigible hangar is now just a giant skeleton.
Originally built in 1933, the huge hangar covers eight acres of land and stands almost 200 feet high, and could cover six football fields beneath its canopy.
Located inside the NASA Ames Research Center in Mountain View, California, the massive structure built to manufacture and hold lighter-than-air craft such as zeppelins, known as Hangar One, remains one of the largest freestanding structures in the world, although it is now simply a skeleton of its former self.