A look at how long the nation's buildings and bridges will stand before the elements consume the steel and concrete, from New York City's skyscrapers to the Gateway Arch in St. Louis, and how once domesticated animals, like horses, will return to wild herds that roam America's grasslands. The episode also examines the ghost town of Rhyolite, Nevada, which was abandoned by people 90 years ago. (thetvdb.com)