The World Trade Center
When terrorists brought down the World Trade Center towers on a crystal clear September day in 2001, horror mingled with disbelief and rage. No one who saw the towers fall will ever forget it. But as time passed, the sight of a skyline without the Twin Towers became more than a reminder of an inconceivably savage attack and the loss of thousands of lives; it also brought home to New Yorkers that somehow, after all, they'd grown fond of that pair of hulking, companionable monoliths anchoring Lower Manhattan.