Damaged in the shocking September 11, 2001, terrorist attacks in which a hijacked commercial jet crashed into the building, killing 125 people working at the Pentagon, and 64 more people aboard the plane, the Pentagon building has been restored, but at this writing, it remains closed for general public tours, although school and military groups may be able to arrange for tours.

The Pentagon is the headquarters of the American military establishment. This immense five-sided structure was built during the early years of World War II. It's one of the world's largest office buildings, housing approximately 23,000 employees. For their convenience, it contains a complete indoor shopping mall, including two banks, a post office, an Amtrak ticket office, a beauty salon, a dry cleaner, and more. It's a self-contained world. There are many mind-boggling statistics to underscore the vastness of the Pentagon -- for example, the building contains enough phone cable to circle the globe three times.