The air was clear, without a cloud in the sky. Businessmen and women hustled to work. Vendors lined the streets. Tourists wound their way around the iconic buildings that make up New York City. It seemed like a normal day.

Mark Eisen arrived at the Old Western Union Building five blocks away from the prestigious 16-acre commercial World Trade Center Complex at about 8:45 a.m. on Tuesday, September 11, 2001. Dressed in jeans and a t-shirt, he was ready to start his workday as a network technician.

Ten minutes later, massive explosions shattered the peaceful Manhattan morning as two commercial airplanes crashed into the city's tallest buildings. Sirens echoed. Lights flashed. Emergency vehicles rushed down Greenwhich Street. Victims screamed. America had been attacked. Within hours, the whole world watched helplessly as the tallest buildings in New York City, which attracted thousands of visitors every year, thundered to the ground, killing 2,823 people.

For months after the attack, a heavy cloud hovered over the city, while the wind blew ash and debris for miles. Many people had such a difficult time coping with the memories and loss that they moved out of the area.

Scattered, New Yorkers mourned alone.

But on the 10th anniversary of that heart-wrenching day, New York City opened the 9/11 Memorial, giving survivors, victims and loved ones a public place to mourn their loss together.

The memorial has been one of the best changes in New York City in 10 years, said Eisen, who now volunteers at the site. Eisen worked in New York for more than 35 years before the attack. He never imagined that the Twin Towers, which stood so majestically at the tip of Manhattan, would ever disappear from the skyline.

Although the towers are gone, the memorial provides a place to remember New York as it was ten years ago, Eisen said.

The 9/11 Memorial, made up of two large, square pools set in the footprints of the original Twin Towers, is a tribute to the victims killed on September 11, 2011 and the six people killed in the much less deadly 1993 attack on the buildings.

Thirty-foot single-stream waterfalls-the largest man-made waterfalls in America-cascade into the pools, gushing into a center void. Rather than one large single waterfall, the memorial includes thousands of smaller streams, each representing the victim's cries and the never-ending grief of their families.

Every day, Eisen walks around the plaza and talks to visitors, answering their questions. He also listens to New Yorkers' stories and shares their grief. They tell tales of lives spared. Some were supposed to have been working at the World Trade Center that day but fell unexpectedly ill and couldn't make it in. Others were supposed to be on one of the planes but switched to a different flight at the last minute.

But Eisen also hears heartbreaking stories of loss. One bereft father came to mourn his son, a 22-year-old college graduate who had just been hired at one of the companies with offices in the World Trade Center. Although his boss insisted that he take the next two days off because of graduation, the eager new employee was too excited about starting work. On his second day on the job, he perished in the attack.

The roaring waterfalls echo in the plaza, drowning out the sounds of the frenetic city. Many visitors tell Eisen the sound of the rushing water represents the victims' helpless cries. Around the pool, the names of the 2,983 victims are inscribed in bronze on the parapet.

"There is not one name more important than another," Eisen said.

The plaza is paved with cobblestones, donated by wealthy contributors. But unlike at other public installations, where contributors names would be inscribed proudly on each brick, the pavers at the memorial are left anonymous, reminding visitors that the only important names are the ones inscribed around the pools.

Although the memorial has been open for less than a year, it already has attracted more than three millions visitors, Eisen said. Earlier this year, Tammy Cusimano, a leader with New Hope Ministries, travelled from Dover, Pa with a van full of middle school students. Many of the students had never been to New York before. In the midst of all the exciting activities that they could choose to do, several students decided that they wanted to pay tribute to the victims at the memorial. Before arriving at the site, the students decided that in commemoration of the victims, they would each select a name and pray for that person's family. For several hours, the students walked around the pools, heads bowed.

"We thought that it would be nice to pray for all the families. It was really a big loss," said Christina Cusimano, a seventh grader. "It makes me feel like I should do something."

As he made another slow lap around the reflecting pools, Eisen said that while 9/11 left a mark of despair on American soil, the memorial has become a beacon of hope-a place of reflection, commemoration, and honor. The tragedy shook the nation but offered him a fresh perspective, Eisen said: "It has given me a better outlook on life."