Tiffney Miller, sister of United Flight 93 victim Nicole Miller, and her mother Cathy Stefani of San Jose, Calif., visit a memorial to Nicole at the Temporary Flight 93 Memorial near the crash site just outside Shanksville, Pa., Sept. 9, 2002. (CNS photo/Jason Cohn, Reuters)
Tiffney Miller, sister of United Flight 93 victim Nicole Miller, and her mother Cathy Stefani of San Jose, Calif., visit a memorial to Nicole at the Temporary Flight 93 Memorial near the crash site just outside Shanksville, Pa., Sept. 9, 2002. (CNS photo/Jason Cohn, Reuters)

Twenty years ago, an abandoned strip mine in western Pennsylvania transformed in one shocking moment into a national shrine, a living testament to the courage of everyday Americans faced with a life-or-death choice.

On Sept. 11, 2001, United Airlines Flight 93 from Newark, New Jersey, to San Francisco was hijacked by four al-Qaida terrorists. The plane's passengers, after learning about other hijacked planes that were flown into the World Trade Center and the Pentagon earlier that morning, decided to fight back and storm the cockpit.

At 10:03 a.m., the plane crashed into the site of the abandoned mine, a field in Stonycreek Township near Shanksville, Pa.

Investigators later estimated the plane was traveling 563 mph when it hit the ground. The crash killed all 44 passengers and crew members, including the four hijackers.

Today, this site is a serene, starkly beautiful memorial, a combination of sights and sounds that offer a testament to the event that changed the profile of this part of Pennsylvania forever.

The dramatic events in the field about 80 miles southeast of Pittsburgh are sometimes hard to convey to those who don't remember them because, unlike the horrors in New York City and Washington, they didn't unfold on live television.

"I think the world and the nation sometimes really don't comprehend what happened here with Flight 93 because there weren't really any vivid live images or any live video associated with the site," said Stephen Clark, superintendent of the National Parks of Western Pennsylvania, which includes the Flight 93 National Memorial.

"We can all remember the jetliners going into the buildings and the Pentagon because we saw it on TV. What was different about Shanksville is most people only remember seeing an image of the smoldering outline and the smoke. What's happened is that over the years the memorial has kind of taken on its own spirit."

The Flight 93 National Memorial site offers more than 400,000 visitors a year many different ways to learn and pay respects to the fallen.

A visitor's center includes a display of artifacts from the site, plus multimedia and interactive exhibits about Flight 93. The memorial plaza allows visitors the chance to walk beside the plane's final flight path and view from a distance the impact site, marked by a sandstone boulder, which can only be visited by family members of the crew and passengers.

One of the most dramatic elements is the newest, Clark said. Opened in 2018, the "Tower of Voices," a 93-foot-high concrete tower filled with 40 wind chimes meant to represent the voices of the fallen, offers a constantly changing tribute of sound that changes with the wind.

All of these elements combine for a unique experience that touches both the mind and the spirit. Clark said the memorial is a popular destination for people of faith who pay tribute to the fallen.

"Sometimes you'll see people praying on their own or you'll see small pockets of people praying silently and holding hands," Clark told Catholic News Service.

He recalled a recent visit by firefighters from New York City and Shanksville that also included family members of people who died in the twin towers and on Flight 93. The group spontaneously prayed the Lord's Prayer together.

"Visitors often come here not knowing what to expect -- they expect maybe to see a crater or parts of the plane -- and they end up leaving here with a real sense of awe," Clark said.

"The memorial fits within the palm of the landscape here. Everything just blends and nothing is out of place. I predict the number of visitors here is going to continue to increase as more and more people around the world become inspired by the story of the people honored here."

The Flight 93 National Memorial is in the Diocese of Altoona/Johnstown, and each year the faithful in the area come together to honor the memory of Flight 93 at special events held around the area, according to Tony DeGol, secretary for communications for the diocese.

The 20th anniversary observances include Masses at both of the diocesan cathedrals. On Saturday, Sept. 11, Bishop Mark L. Bartchak will celebrate Mass at the Cathedral of the Blessed Sacrament in Altoona. On Sunday, Sept. 12, a special Blue Mass honoring local police officers, firefighters and emergency medical services will take place at St. John Gualbert Cathedral in Johnstown.

Bishop Bartchak and others from the diocese will also attend a community tribute on the evening of Sept. 11 in Altoona which will include speakers, special music and a Walk of Honor to pay tribute to local first responders, military members and Gold Star families, who had a family member die while serving in the military.

"The three components of the celebration are going to be faith, patriotism and civic pride," DeGol said. "We especially recognize the faith component is so critical because since 2001 it has helped us all as we've tried to cope with what happened that day and the lives lost on that day."

To learn more about the history of Flight 93 and commemorations of the 20th anniversary, visit the national memorial's site at https://www.nps.gov/flni/index.htm or Friends of Flight 93: https://www.flight93friends.org/.