MAMARONECK, N.Y. – Fifteen years after the Sept. 11, 2001, attacks decimated the twin towers in lower Manhattan, the 1,776-foot One World Trade Center rises out of the ground, a palpable symbol of triumph and optimism. The tallest skyscraper in the Western Hemisphere is the soaring, storied, centerpiece of a 16-acre complex that includes eight other major structures.