The National 9/11 Memorial & Museum
Architects Michael Arad and Peter Walker were the winners of an international competition to design the space where the World Trade Center once stood. Their proposal, called Reflecting Absence, consists of two pools that sit in the footprints of the South and North Towers. They're fed by waterfalls (the largest manmade waterfalls in the United States) and surrounded by a forest of nearly 400 trees.
The 9/11 Museum has an exhibition divided into three sections, the Day of 9/11, Before 9/11 and After 9/11. It uses artifacts, photos and an extensively researched and laid out collection to show how the events of 9/11 changed the world.