NEW YORK — President Barack Obama and Sept. 11 survivors, rescuers and victims’ relatives are expected to mark the opening of the 9/11 museum, where the story of the terrorist attacks is told on a scale as big as the twin towers’ columns and as intimate as victims’ last voicemails.

The National September 11 Memorial Museum is set to be dedicated Thursday before opening to the general public May 21.

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.

“You won’t walk out of this museum without a feeling that you understand humanity in a deeper way,” museum President Joe Daniels said Wednesday.

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.

And its opening is prompting reflection from presidents and the everyday people whose lives were changed by the attacks.

Obama is mindful of “the need to remember and the power of memory in a nation’s history, as well as the need to properly grieve and rebuild,” White House spokesman Jay Carney said Wednesday. Former President George W. Bush issued a statement saying the museum “will help ensure that our nation remembers the lessons of Sept. 11.”