The idea that a buildings walls will stand up seems as safe a bet as gravity's pull or the suns rising. Most of US don't worry much about whether our apartments, offices, supermarkets, or schools are going to collapse on US as we go about our daily routines. But should we? National Geographic takes a look at buildings around the world that despite having appeared structurally sound, some for years on end, came crashing down in a moments notice. Dig deep into the histories of these buildings to discover why.