The Boeing Everett factory tours are conducted to showcase The Boeing Company and the Everett product line, the 747, 767, and 777. As part of the tour, visitors will be located in the largest building in the world by volume (472,000,000 cubic feet). On the Boeing flight line, visitors will see airplanes in various stages of flight test and manufacture for airline customers around the world. Visitors come from every walk of life and from every region of the globe, all with a common interest -- to see the number one aerospace leader in the world: The Boeing Company.
http://www.boeing.com/companyoffices/aboutus/tours/