One of the 911 Memorial Reflecting Pools. Two massive reflecting pools were designed to sit exactly in the footprints of the original Twin Towers at the site of the September 11 attacks. The memorial’s overall design is called “Reflecting Absence.” At the center of each pool is a dark square void into which the water disappears. Arad, the designer, described the pools as “absence made visible.” The idea was that the loss left by 9/11 can never truly be filled. Water endlessly flows into the voids, but the emptiness remains. The waterfalls are the largest man made waterfalls in North America.