St. Paul's Chapel, next to Ground Zero, serves for many as an interim memorial.
Though it was carpeted in dust and debris, it escaped serious damage and became a center for rescue workers as well as a shrine where desperate relatives would leave flyers with photos of the missing, flowers, candles, poems and other gifts.
Many are still on display, along with computer terminals that allow a visitor to watch video clips of key moments in the aftermath. The church holds daily prayers for the victims and will hold an interfaith service on Monday.
Church worker Omayra Rivera, 33, said around a million visitors a year come to St. Paul's. "They (church officials) don't use the word 'tourists,' they say 'pilgrims."'
Thousands of tourists congregate from morning to night every day on the west side of Ground Zero, peering through the fence, taking pictures, silently reading a timeline of the events of 9/11, and fending off the occasional peddler hawking collections of photographs of the attacks.
Souvenir sellers have been ordered out of the immediate area, though fire and police department T-shirts and caps as well as key-rings and bottle openers in the shape of the Twin Towers can still be purchased a few blocks away.
Some visitors choose to leave something behind.
One message scrawled on one of wooden walkways around the site reads: "Yo, New York. I hope you are feeling better. I see that nasty scar is starting to heal ... a ... little."