Willow Run was an enormous Ford automobile factory that was converted to produce B-17s and B-24s during the Second World War. Today the building that was used to build the B-24s has been converted to an enormous hangar that houses, among other things, the Yankee Air Museum. I paid a visit there yesterday...
Here is Willow Run when they were churning out B-24s:
Here it is today from about halfway down the buidling:
Here are a couple of the Y.A.M. aircraft. The Yankee Lady (B-17):
The Yankee Warrior (B-25). There is a 707 trainer/simulator in the background:
They're still restoring their B-24. It's just an airframe now (no pic - sorry).