NEW YORK >> President Barack Obama praised the new Sept. 11 museum on Thursday as "a sacred place of healing and of hope" that captures both the story and the spirit of heroism and helping others that followed the attacks.

"It’s an honor to join in your memories, to recall and to reflect, but above all to reaffirm the true spirit of 9/11 — love, compassion, sacrifice — and to enshrine it forever in the heart of our nation," he told an audience of victims’ relatives, survivors, and rescuers at the ground zero museum’s dedication ceremony.

"Like the great wall and bedrock that embrace us today, nothing can ever break us. Nothing can change who we are as Americans."

After viewing some of the exhibits, including a mangled fire truck and a memorial wall with photos of victims, the president recounted the story of Welles Crowther, a 24-year-old World Trade Center worker and former volunteer firefighter who became known as "the man in the red bandanna" after he led other workers to safety from the trade center’s stricken south tower. He died in the tower’s collapse.

One of the red bandannas he made a habit of carrying is in the museum, and Crowther’s mother, Alison, told the audience she hoped it would remind visitors "how people helped each other that day, and that they will be inspired to do the same in ways both big and small. This is the true legacy of Sept. 11."

By her side was Ling Young, one of the people Welles Crowther rescued.

"It was very hard for me to come here today, but I wanted to do so, so I could say thank you to his parents," she said.

Before the ceremony, Obama walked quietly through an expansive hall with former New York Mayor Michael Bloomberg. First lady Michelle Obama, former President Bill Clinton and former Secretary of State Hillary Rodham Clinton following behind them.

The museum, which commemorates the 2001 terrorist attack, as well as the 1993 World Trade Center bombing, opens to the public on May 21.

New York Gov. Andrew Cuomo, New Jersey Gov. Chris Christie, current New York Mayor Bill de Blasio, former Mayor Rudy Giuliani and former New York Gov. George Pataki were among those attending, as was actor Robert De Niro, a museum board member.

By turns chilling and heartbreaking, the ground zero museum leads people on an unsettling journey through the terrorist attacks, with forays into their lead up and legacy.

There are scenes of horror, including videos of the skyscrapers collapsing and people falling from them. But there also are symbols of heroism, ranging from damaged fire trucks to the wristwatch of one of the airline passengers who confronted the hijackers.

"Walking through this museum can be difficult at times, but it is impossible to leave without feeling inspired," Bloomberg said Thursday.

The museum and memorial plaza above, which opened in 2011, were built for $700 million in donations and tax dollars. Work on the museum was marked by construction problems, financial squabbles and disputes over its content and the appropriate way to honor the dead, but its leaders see it as a monument to unity and resilience.

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Associated Press writer Josh Lederman contributed to this report.