NEW YORK - It's one thing to have watched the World Trade Center collapse on television, gaping as the huge ash cloud swirled down the street. It's quite another to have been there, and then trampled and nearly suffocated trying to outrun the debris.

That was the thought that crossed Jim Jenca's mind last week as he wandered through the National September 11 Memorial Museum during a special opening for survivors and victims' families. It's not that he felt unmoved by the onslaught of videos and artifacts, or the photographs of dead friends, the Levittown resident explained, "but in a strange way, I realized, it's something I'd already seen. It was less traumatic than the horror of experiencing it."

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For the rest of us, a trip to the underground museum, which opened Wednesday, will be as close as we come to the raw, you-are-there terror of that day when hijackers rammed airliners into the twin towers, reducing them to a heap and killing 2,983 people. My advice: Bring tissues.

Into the abyss

The exhibit is unlike almost any other, save the U.S. Holocaust Memorial Museum. But in this case, we are still living in history, still trying to come to terms with emotions whose shelf life has yet to expire. Reviewing the building as architecture didn't seem right, so I asked Jenca to serve as my Virgil on the descent into the abyss of memory and Manhattan schist.

After the South Tower was hit, Jenca, 53, a security expert for Credit Suisse First Boston, was dispatched to the Port Authority's underground command center to coordinate the company's evacuation. He never made it.

Jenca was walking around the corner of Church and Fulton Streets, next to Trinity Church, when the building collapsed. As an immense ball of ash hurtled through the narrow streets and thousands ran for their lives, he was knocked to the ground. What he remembers next is waking in a triage station with a damaged lung and twisted knee.

Once a regular on Amtrak's 6:20 a.m. train from Trenton to Manhattan, Jenca hasn't made the commute since. He left his job a few days later and went on disability in 2004. Had he reached the command center, his ruddy face would have been among the nearly 3,000 photographs staring down from the walls of the museum's memorial pavilion.

The museum, which has been beset by controversies, delays, cost overruns, and even flooding from Hurricane Sandy, tries its best to be all things to all people: a somber memorial, a history exhibit, a mausoleum for unidentified remains. It actually does a heroic job of straddling the competing demands. You will almost certainly end up weeping.

And yet, for all its lurid hold, the museum offers no reckoning, no lessons, no real insights into why those planes fell from that brilliant-blue autumn sky. The tone is not triumphal, but rather blandly neutral, even in the section discussing the rise of al-Qaeda. The museum is content to re-create the day and replay it in an endless loop.

Even if you were glued to the TV on 9/11, the video and artifacts will startle. At one point, Jenca stood transfixed watching a slow-mo replay of the plane hitting the South Tower. "Everything is so real," he murmured.

Videos have been coupled with audio, amping up the visitor experience in a chilling way. As you watch the towers turn into fireballs, you hear the mounting panic in the voices of first responders. Voice-overs from survivors cut in, while the low, steady wail of sirens keeps up in the background.

It is hard to take it all in, and not just because of the subject matter. The exhibit designers, who had to cull the remains of two skyscrapers, clearly had a hard time leaving things out. The galleries sprawl over 110,000 square feet - three times the space the Holocaust museum devoted to six million deaths.

Designed by Snøhetta and Davis Brody Bond, with exhibits by Thinc Design, the museum is conceived as a journey down to bedrock, seven stories below the surface. The route follows the ramp that was built to remove the debris, and it weaves between aluminum-sheathed cubes, located where the foundations of the towers once stood. You come face to face with the retaining wall that miraculously held back the Hudson River after the attack.

The descent is clearly meant as a metaphoric trip into the underworld. It offers very little uplift, though there are a few moments. It helps to be reminded of the first responders' willingness to wade into the inferno. Seeing the victims' wide spectrum of ethnicity, race, and nationality is also a solace. They are the symbolic bedrock of the nation.

The cubes divide the museum into its parts: a memorial and history exhibit. The artifacts range from splayed steel to a crushed fire truck to the contents of victims' wallets. Random rewards cards and receipts from birthday dinners may be the most heart-wrenching displays.

Jenca made a beeline for the cube housing the victims' memorial. It is surrounded by a moat - a metaphoric River Styx - where you can see the severed outlines of the columns that supported the towers. You must cross a low bridge to enter, passing through the invisible perimeter of the towers.

Jarring moments

Once inside, Jenca scanned the faces, stopping when he saw Robert Lynch, the Port Authority liaison he was supposed to meet in the command center. "What happened to me pales," he began, his voice trailing off.

Leaving the memorial, he bumped into Gen. Mark S. Martins, who is prosecuting five men charged with masterminding the attack. Jenca got to know Martins after he traveled to the base at Guantánamo Bay to observe the proceedings. "All these years, and justice has not been brought," he told me later. "It's disgusting."

In the days after the attack, many wondered whether the world would ever recover. Today, the block above the museum is a clanging construction site, where three office towers are rising. Hordes of visitors crowd the memorial park, before heading to Century 21, a discount clothing store - an odd marriage of the tragedy tourism and consumer tourism that emerged after the attack. At the same time, the museum is taking a beating for including a gift shop in a place that is part graveyard.

Meanwhile, in the bowels of the museum, it can seem as if time has stopped since 2001. Little is said about the aftershocks of wars and economic collapse.

There is, however, one indication that the world has changed utterly since then. Entering the museum, you arrive in an unexpectedly stark room, painted institutional gray. You are welcomed to the 9/11 museum by an array of security screeners and the glass cylinder where you throw your hands up in mock surrender. No one was deterred by their presence. We all knew exactly what to do.