The Pentagon is a five-sided military compound and headquarters of the United States Department of Defense. The Pentagon is not far from the Potomac River and Ronald Reagan National Airport just across the river from Washington, D.C. in Arlington, Virginia. It is home to the offices of the U.S. Joint Chiefs of Staff, the Secretary of Defense, and the Joint Terrorism Task Force.
Ground was broken at the Pentagon on September 11, 1941, in order to house the 17 offices of the War Department in the lead up to World War II. Within 7 months, the site was ready for occupancy and the entire building was completed in 17 months. The site was the largest office building in the world, with three times the office space of the Empire State Building. At its peak in World War II 35,000 people worked at the Pentagon.  The Pentagon was constructed with twice as many restrooms as needed, to accommodate the Virginia segregation laws.
During the Vietnam War a number of Protests against the Vietnam War occurred around the Pentagon. One of the most colorful of which occurred on October 20th 1967, when Abbie Hoffman led a group of approximately 50,000 protesters in an attempt to exorcise the Pentagon of demonic influences—Hoffman said that if successful this attempt would cause the Pentagon to levitate, rotate mid-air, and turn orange. 
On September 11, 2001, terrorist organization Al Qaeda crashed a passenger aircraft into the Pentagon, in an apparent attempt to destroy the building, as part of their 9/11 attacks. During the terrorist attacks, hijackers crashed American Airlines Flight 77 into the west side of the Pentagon. The crash damaged three of the five sides of the Pentagon. Because the affected area was under renovation at the time, several offices were unoccupied, sparing many lives. The Pentagon has since been repaired and the first workers whose offices were damaged in the attack began moving back in on August 15, 2002, nearly a month ahead of schedule. At the center of the compound is a snack shop called the Ground Zero Cafe which sells sandwiches and coffee.