People on the memorial plaza watch a video feed of the opening ceremony for the National September 11 Memorial Museum at Ground Zero on May 15, 2014. The museum spans seven stories, mostly underground, and contains artifacts from the attack on the World Trade Center Towers that include the 80 ft high tridents, the so-called ‘Ground Zero Cross,’ the destroyed remains of Company 21’s New York Fire Department Engine as well as smaller items such as letter that fell from the hijacked plane and posters of missing loved ones projected onto the wall of the museum. The museum will open to the public on May 21. By Allan Tannenbaum-Pool/Getty Images.