Thirteen years after the 9/11 attacks, One World Trade Center is now officially open. The first tenant, Condé Nast, moves its headquarters to the building on Monday (3.11.2014). More than 3,400 editors, writers and advertising executives at its 18 magazines, which include the "New Yorker," "Vogue" and "Vanity Fair," Condé Nast are moving to the building from Times Square.

One World Trade Center, a 104-storey skyscraper, cost $3.9 billion to build, according to AP's report. Much like the iconic Twin Towers that were destroyed in 2001, it now dominates the Manhattan skyline.

The 540-meter high tower was initially set to open in 2006 but became fraught with delays and political squabbles. For many, it symbolizes hope and a resurgence of the New York City skyline and the American society in general.

"The New York City skyline is whole again," Patrick Foye, executive director of the Port Authority of New York and New Jersey that owns both the building and the World Trade Center site, told AP. "The opening of this iconic building is a major milestone in the transformation of Lower Manhattan into a thriving 24/7 neighborhood," he added.

From the northeast corner of the site, the tower overlooks the National September 11 Memorial and Museum. .

World trade center is trending on social media - they were more than 800 tweets in an hour at 11:20 (UTC) according to Topsy.