One World Trade Center (also known as One WTC or Freedom Tower) is the main building of the new World Trade Center complex in Lower Manhattan, New York City. The building is tall making it the tallest building in the Western Hemisphere. Since late 2013, it is the tallest building in the United States. It opened in late 2014. It is mostly used for offices. People can view the city from an observatory near the top. The building was designed by David Childs of Skidmore, Owings &amp; Merrill.