As diplomats from around the world gather this week at the United Nations headquarters in New York City for the annual General Assembly meeting, they are encountering a rare sight: scaffolding hung from buildings’ exteriors. After years of intense preparation, the 17-acre U.N. campus is undergoing its first major renovation since it was erected along the East River shortly after World War Two.

The sweeping renovation won’t come cheap, at $1.87 billion, with the cost to be split among all 192 member nations. But when it’s complete in 2015, the five-structure complex, whose 11-member design team included Le Corbusier, Oscar Niemeyer, and Wallace K. Harrison, may look more Modernist than it has for decades.