According to Streetsdept, the Budd Factory is a former industrial plant located in Hunting Park, Philadelphia. It is currently abandoned and includes a network of 20 buildings covering over 75 acres. At its peak, it held approximately 2.1 million square feet of space. That's one hell of a space.
The next time I go to Philly, I'm visiting this place for sure. And eating Federal Doughnuts. Here's a video from inside.