Downtown Manhattan is resurgent 10 years after the 9/11 attacks. The residential population has doubled; two skyscrapers are rising at Ground Zero, due to open in 2013; and the national memorial is open. But the cost of rebuilding the trade center and surrounding areas run to $24 billion. One World Trade Center alone cost $3.2 billion to build. Security concerns contributed to the building’s being redesigned three times in the last 10 years. Yet, after years of delays, the progress of the rebuilding has given hope to many. "Things are actually coming along very well," said John H. Mollenkopf, director of the City University of New York's Center for Urban Research.