Tragedy struck the United States on September 11, 2001 after terrorists attacked not only New York City, but also the Pentagon Building outside D.C. This simple yet elegant memorial, built along the side of the Pentagon that was hit, was dedicated in 2009. Each of the 184 steel-and-granite benches are labeled with the names of the 184 victims, arranged from youngest to oldest. Looking at the person's name at the end of the bench and the sky signifies that he or she was on the flight, whereas seeing both the name and the Pentagon signifies that that person was in the building at the time of the attack.
Photography is permitted within the memorial, but for security reasons, avoid pointing your camera at the Pentagon Building itself.