The annual Stephen Siller Tunnel to Towers run is an emotional moment for many people, including firefighters from around the country, as they walk in the footsteps of a true hero.

The sneakers hit the road at the 14th annual Tunnel to Towers run in honor of Stephen Siller, a New York firefighter who ran from his car on the Brooklyn side of the Battery Tunnel to the World Trade Center towers on September 11, 2001, and was killed when the towers fell.

"You hear the spirit behind is unbelievable," said Frank Siller, chairman and CEO of the Tunnel to Towers Foundation. "So this is a celebration of life. It's a memorial celebration, but it's a celebration of their lives."

An estimated 35,000 people participated in Sunday’s run, many more than when the event started in 2002 with about 300.

Over the years, the run has raised millions of dollars to help severely injured service men and women when they return home from the military.

"It's humbling. It's a big thing," said Patrick Scullin of the Tunnel to Towers Foundation. "The foundation started around a coffee table, my family, my mother and her siblings."

"It's the first time I've done this," said one participant. "I'm overwhelmed. I actually was crying before, almost, because this is just, it's an emotional experience for everybody."

The tunnel connects Brooklyn to Manhattan, just like this run, is connecting the coasts, from New York to California. We caught up with a Los Angeles firefighter just as he crossed the finish line.

"The brotherhood came together, and I'm just very proud to be part of the fire service and to honor Stephen today," he said.

"Even on the West Coast, where I'm from, we still have not forgotten," said another participant.

"It's an incredible feeling of solidarity, and it really gives us a sense post-9/11 that despite all the infighting, we really are one and we can come together," said a third.

While runners are still recovering from the run, organizers are already gearing up for next year's event.