Skyscrapers have transformed cities across the globe - most notably the famous skyline of Manhattan. But on 9/11, this historic cityscape became forever linked with one event that forced architects to rethink. Designed by skyscraper guru David Childs, from renowned architects SOM, 7 World Trade Center is the first building to be constructed on Ground Zero and it has taken skyscraper safety to new levels. But overlooking a plot of land that symbolises the risk of building tall, do those who work in it really feel safe?