Many see them as massive testaments to America's progress. Some view them as immutable symbols of the human spirit. Others perceive them as sacred shrines dedicated to the ideals of liberty and freedom. But no matter what they represent--America's monuments are inarguably impressive due to their colossal size and scope, their groundbreaking feats of engineering, and their storied histories. Why is it that America's greatest monuments continue to enthrall us decades--and sometimes centuries--after their creation? And perhaps more importantly, what closely guarded secrets may their implacable facades be hiding?