You descend into the museum on a long ramp, sloped so gradually that you barely feel your steps gathering momentum. It’s as if you’re gently being pulled into orbit. Then you walk out onto an underground balcony overlooking the museum floor, some 40 feet below, and gaze out into a vast, nearly empty space punctuated by the Last Column—the final piece of steel hauled away from Ground Zero during cleanup. Weighing 60 tons and standing nearly 40 feet high, it’s still covered in spray-painted messages, tributes to the dead left by those who did the work. (“My brothers, you ran into hell,” one reads.) You get an overwhelming sense of absence and awe. There may be no public space more cavernous in New York City, and the vista was designed to preserve the dizzying experience of looking into the gaping pit left when the cleanup was complete in the spring of 2002.

To your left is the Slurry Wall, a 3-foot-thick concrete barrier studded with iron pilings that once girded the foundations of the site and managed to hold even after the towers fell. The wall still seems both immovable and ­fragile. It’s what keeps the Hudson River from drowning this space, which is an unprecedented hybrid of archaeological site, cathedral, and tourist attraction.

As you keep walking downward, the ramp switches back, and you pass by a quote rendered in metal letters 15 inches high and cast from steel recovered from the original Twin Towers: NO DAY SHALL ERASE YOU FROM THE MEMORY OF TIME. It’s a line by Virgil, who, in the Inferno, serves as Dante’s guide through hell. Stepping off the ramp and passing down a flight of stairs and a hallway, you are now 70 feet belowground, standing on the bedrock that rooted the Twin Towers.

Twenty feet above your head hangs a piece of steel more than 35 feet long and weighing nearly 5 tons. It’s positioned vertically on the side of a massive silvery cube that marks the outline of where the North Tower once stood. Twisted like a ribbon blown in the wind, it has a ter­rible beauty. This and a counterpart down the hall are the “impact steel,” the columns hit by the first passenger jet when it slammed into the North Tower almost 13 years ago. You pass under one of the steel pieces and through a pair of plain glass doors to enter the main exhibits of the National September 11 Memorial Museum.

Historical museums typically serve as a way to tell the official story of something that happened and what it means. This one is different. “It is a story that has no end,” says Paula Grant Berry, a ­museum-­planning-­committee member whose husband died in the South Tower. The events of 9/11 are still raw in our memories and alive in our political and cultural climate.

For the museum’s designers and curators, that tension led to a ­tangle of quandaries: How can you present a lasting memorial to an event whose impact is still unspooling through developments such as the Edward Snowden leaks and the Senate’s torture report? How can you speak to 9/11’s polarizing effects, such as the ­bungled search for WMD, without alienating some significant portion of your audience? How can you create a meaningful tribute that will resonate with every visitor: the school­children who know almost nothing of what happened, survivors who ran from the buildings covered in ash, and all those—more than a billion worldwide—who experienced the attack live on TV? “Conventional narrative wouldn’t cut it,” says Alice Green­wald, director of the museum, which opens in May.

Perhaps the most vexing problem of the project’s design, which incorporates thousands of artifacts, is that it risked becoming one massive trigger for victims and a trauma in its own right for everyone else. “This is not the Disney World of 9/11,” says Green­wald, a petite, dark-haired woman whose room-­filling good cheer belies the material she has absorbed and calibrated. “We weren’t going to immerse ­people in the experience.” As Jake Barton, founder of Local Projects, which helped design the space, says, “That was the first, panicking challenge: How do you rise to the event itself for the ­people who lived it without overwhelming everyone else?” The fear of seeming hasty or naive was almost paralyzing. “Usually, as designers, you try to create meaning. Here there was almost too much of it,” Barton says.

The museum’s creative team ­tackled these emotional and psychological challenges through a combination of sophisticated design and artfully deployed technologies: a data-mining algorithm, onsite digital recording booths, a web-based platform for gathering crowdsourced testimony, touchscreens that let you access remembrances of the dead. The result isn’t so much a record of an event as a testament to how much we’ve all witnessed—no one more so than the survivors and family members, whose experiences are almost impos­sible to imagine until you hear from them yourself.

Foundation Hall | The last column stands wrapped in protective canvas. The installation called timescape is projected on the wall behind it. Vincent Fournier

The museum began to take shape eight years ago in a generic office on the 20th floor of One Liberty Plaza. In late 2001, the room, which features a view of Ground Zero, was set aside by the Lower Manhattan Development Corporation as an interim memorial space for the families of victims. The windows and walls were soon papered over with remembrances. To glimpse Ground Zero at all, you had to peer through the narrow spaces between pictures of ­people who had died. Many were small framed photos like the ones you’d see on a nightstand; a few were kids’ drawings with pictures ­stapled to them. At the center of the room was a podium bearing an oversize guest book filled with notes written to the dead. It remains in place today, off-­limits to everyone except families. (A new private family room in the museum will replace this one later in 2014.)

Tom Hennes first visited the room in 2007, soon after his firm, Thinc, won the original museum commission. It felt like a time capsule. Hennes remembers that the notes were written in the present tense; one woman wrote to a relative asking for his approval of her new boyfriend, whom she’d brought with her. “The room tuned us in to what trauma means,” Hennes says. “Time had stood still.”

To the designers, the very rawness and variety of expression suggested an answer to a central challenge: how best to present events when, as William Faulkner once wrote, “the past is never dead. It’s not even past.” Instead of providing its own interpretive explanations, the designers realized, the museum could focus on direct testaments from the ­people who had experienced it. The hope was to avoid a ­single story line and instead allow visitors to reconstruct narratives on their own, using the artifacts on display. “Witnesses are the way into the museum,” Green­wald says.

It was an approach that Barton had been inching toward for more than a decade, influenced by such Anna Deavere Smith plays as Twilight: Los Angeles, 1992. For that meditation on post–­Rodney King racial resentments, Smith conducted more than 300 interviews and then condensed the material into four dozen characters. She portrayed each of them herself, one blending into the next. “It was a lightning bolt,” Barton says. “It was really an exercise in empathy, in trying to find the humanity of everyone involved.” Ever since, Barton has used this as his inspiration in commissions that integrate mul­tiple narrators. For ­example, Local Projects designed the oral history booths for Story­Corps, a project that is collecting thousands of personal stories and archiving them at the Library of Congress.

The Goal: Create A Meaningful Tribute to the Victims without Traumatizing the Visitors.

Voices are the first thing you hear in the museum, in the vestibule that precedes the entrance ramp: 417 ­people completing one another’s sentences. These are not from the victims but ­from people around the world who contributed their own 9/11 recollections via phone, video, or a web-based platform. Their words are mapped to hundreds of cities across the globe and then projected onto a series of staggered panels. As you walk around and stand in front of the screens, the words project around you, enveloping you in their stories.

Visitors are invited to bear witness again as part of Reflecting on 9/11, one of the museum’s signal installations. It consists of videos projected on massive walls and featuring interviews with figures who shaped our responses to 9/11, from the head of the ACLU to then defense secretary Donald Rumsfeld. They answer intentionally broad questions such as, how do you balance national security and personal freedom? Visitors, in turn, can answer the same questions in their own booths next to the installation. The curators can then pick visitor responses to display on the main wall.

But the same intimacy that makes all these voices so powerful can also make them overwhelming. The curators had access to thousands of hours of recordings of witnesses, survivors, and victims—voicemails, 911 calls, even radio call-ins. These posed a dilemma: Experts like Billie Pivnick, a clinical psychologist who worked closely with the designers, warned that hearing victims’ voices in the throes of terror could traumatize listeners. Even for the designers, direct access to the material proved difficult. “It felt like being a war correspondent,” Barton says. He recalls having persistent nightmares about buildings crumbling. Some ­people on Hennes’ team burst into tears at unexpected moments, unable to explain why the material, which seemed so familiar one day, was intolerable the next.

With this in mind, the curators had to decide which recordings were appropriate. For ­example, they opted not to include a 911 call from a woman trapped on a high floor who knew she wasn’t going to survive; the call ends with her simply praying with the operator. They did decide to include a voicemail that 24-year-old Brad Fetchet left for his mother minutes after the first plane hit the North Tower. “Hey, Mom. I’m obviously alive and well but obviously pretty scared … Love you.” Fetchet died in the South Tower. Green­wald admits that these were judgment calls. The choices usually favored the recordings in which ­people, even those who died, seemed most in control.

Chosen Paths ————

The 9/11 Memorial Museum uses technology and artful curatorial techniques to bring personal testimony to the fore without overwhelming visitors’ emotions. Here’s how the curators pulled it off. —C.K.

Bryan Christie Design

Historical Exhibition The bulk of the material lies in a chronological exhibit of media and artifacts about 9/11. 1 | Day of the Attacks Visitors follow the day’s events starting at 8:46 am on September 11, 2001, the moment the first plane hit the North Tower. Alcoves house the most emotionally sensitive material. The toughest exhibit to create was the one that depicts the people who jumped or fell from the towers. To avoid aestheticizing the event, designers stripped the display of nearly all adornment. 2 | Looking Back The museum then turns back the clock to understand the history leading up to 9/11, showcasing artifacts like a laptop used by the FBI as evidence linking the 1993 World Trade Center bombing to al Qaeda and the 2001 attacks. 3 | Aftermath This is where visitors follow the recovery after the attacks, viewing such artifacts as a preserved storefront covered in dust, and steel that was mangled in the burning towers’ collapse. 4 | Reflecting on 9/11 Here visitors can watch key figures such as Eric Holder and Donald Rumsfeld answer questions about how the attacks affected government and society.

Location The National September 11 Memorial’s twin reflecting pools (squares) mark the footprints of the North and South Towers aboveground. The 9/11 Memorial Museum lies below.

Memorial Exhibition The ­people who died on 9/11 and in the 1993 World Trade Center attack are remembered in pictures mounted on the perimeter of the room. Visitors can see and hear materials from an ever-­expanding archive in an inner chamber designed to encourage eye contact among visitors.

Last Column Standing nearly 40 feet high, the Last Column was the final piece of steel removed from Ground Zero. At the museum, touchscreens allow you to pan around images of the entire column so you can read inscriptions alongside annotations of the stories behind them.

Exposed Box Columns The original steel columns, once used to anchor the North Tower to the bedrock, have been sheared to floor level here.

Timescape An algorithm collects headlines related to 9/11 and projects them on a concrete wall, evoking the attacks’ effect on current events.

That element of control is emphasized in the museum’s layout, which allows visitors to decide how much of the most emotionally provocative moments they will experience. The main path through the historical exhibit is dominated by physical artifacts—a storefront preserved from a block adjacent to Ground Zero (complete with dust-­covered blue jeans and sweatshirts emblazoned with American flags), the hand rakes used to sift the site for remains, mangled steel from the building. But the curators ­struggled most with how to present hundreds of more personal audio recordings and visual records. In the end, they decided to put this sensitive material inside alcoves placed off the main pathway through the exhibit. To confront these collections, you have to seek them out.

The most difficult alcove to design was the one dedicated to the ­50 to 200 men and women—the exact number is not known—who, overwhelmed with heat and smoke, jumped or fell from the buildings. “Those ­people were on a ledge and feeling like they had no option but to step into a sky that would not support them,” says Joe Daniels, president of the 9/11 Memorial and Museum. “It is so unbelievable. Maybe you don’t show it.” And yet, after much intense debate, the board overseeing the museum, including Daniels, voted unani­mously to dedi­cate an exhibit to those victims.

Some suggested a ­simple text panel and a statistic printed on the wall, nothing more. Others thought the video footage had to be used. Between these poles of detachment and immediacy, Green­­wald says, was a limit­less range of possibilities. One initial, commonsense idea gathered support: Mount pictures of ­people falling, in ­simple frames. And yet the effect, once tested, was horrifying. “It was the equivalent of a gallery display,” Green­wald says. “It aestheticized the moment. We recoiled from it.” They tried video in turn, and this created a gruesome loop as the event ran to its awful conclusion over and over.

The exhibit that finally emerged after dozens of prototypes is so artful that it seems almost totally undesigned. The entrance is marked by a photo of a small group of ­people on the street, looking up in shock. One woman is gazing just past the camera, covering her mouth. “There were a ­couple of instances when we said, there is no other photo pos­sible,” Green­wald says. “You know from this photograph what they’re looking at.” Once you step into the alcove, you see a ­single picture, mounted on a stout column that dominates the center of the room. Titled “Trapped,” it shows men and women leaning out of the towers’ broken windows, with black smoke streaming out from behind them. On the walls surrounding you are quotes from ­people who witnessed victims jumping or falling:

They were ending their life without a choice, and to turn away from them would have been wrong.

This woman stood there for what seemed like minutes, then she held down her skirt and then stepped off the ledge. I thought, how human, how modest, to hold down her skirt before she jumped.

You won’t see anyone falling unless you make your way around the big column to a nook at the back of the room. There, 3 feet above your head, are projected a series of five still photographs of ­different people falling from the towers. They fade from one to the next, in a slow progression that gathers no rhythm. “We don’t ask the person jumping to repeat the act over and over again,” Green­wald says.

That room, designed by David Layman, made it pos­sible to present potentially explosive imagery without glossing it over or causing offense. But when it came to presenting the ways that 9/11 shapes political debate, current events, and news coverage, the curators resorted to a different tool altogether: an algorithm. “The system lets the curators say they haven’t set an agenda,” Barton says. The algorithm, coded by Local Projects, sifts through the news of the day, finding nuggets relating to 9/11 and extracting connections among them. Its output is projected on a concrete wall as an enormous graph some 34 feet across. Dubbed Times­cape, it is a constantly evolving chart of news ­articles connected to 9/11. At times it looks like a spray of data points charted against two axes: time versus frequency. Each point is labeled according to a topic or theme, from lead hijacker Mohammed Atta to the Snowden leaks. As the display cycles, each theme is unfurled in a new, more detailed chart that reveals the series of headlines that relate to it.

Academic researchers and even the Associated Press have experimented with using similar data-­mining technologies to sift through massive document archives such as the Chelsea Manning leaks. But Local Projects wasn’t sure any of them would work for the museum. Confirmation came suddenly when Dylan Fried, one of the programmers coding the algorithm, was checking the themes and ­articles the machine was culling line by line. Fried, only 11 years old at the time of the 9/11 attacks, came upon a funny acronym and Skyped a colleague: “Who’s this KSM guy?” He was, of course, Khalid Sheikh Mohammed, master­mind of the attacks, and he kept popping up as a detainee at Guantanamo Bay and linked to the 2002 Bali nightclub bombing. “This algorithm showed Dylan a whole world of connections,” says Sundar Raman, Fried’s colleague. In other words, it worked.

The algorithm’s precision offers startlingly sharp insights about the ebb and flow of current affairs. It doesn’t elide what’s there, and it doesn’t overplay or underplay some themes for emphasis, as a curator inevitably would. It simply shows events for what they are, in news headlines. In that way, its effect is akin to the polished black granite of the Vietnam Veterans Memorial, which allows visitors to see their own reflections atop the inscribed names. Architectural critics have given almost metaphysical weight to the fact that the memorial’s ­marble literally mirrors the present day. At the 9/11 Museum, the mirror is a math equation.

Moral philosopher Avishai Margalit, in his meticulously reasoned book The Ethics of Memory, wrote, “We need morality not so much to counter evil as to counter indifference.” By that measure, a museum like this one must aim to shake the familiarity that robs us of our shock and horror, blunting our moral reactions. Tom Hennes, who’s something of a museum radical, echoed that idea from the start. He doesn’t believe museums should be venues for education but rather places of encounter. He offers an ­example: “Natural history museums are lousy at teaching natural history,” he says. “But they can provide a new sense of wonder that changes your next walk in the woods.”

Hennes is proudest of the museum’s memorial, which lies apart from the historical exhibit, in the footprint of the South Tower. He and Barton designed the space, which presents stories and artifacts provided by the fami­lies of victims. The challenge was to somehow satisfy all the families, each of whom may have envisioned a different form of memorial. Hennes and Barton’s solution is not a grand architectural gesture, just a ­simple square room of about 3,000 square feet.

Upon entering, you are surrounded by the faces of those who died, shown in mounted photos arrayed in neat alphabetical rows, from floor to ceiling, on all four walls of the room. In the center are the four walls of another, smaller room of about 700 square feet. In the space between the outer and inner walls there are waist-high tables embedded with touchscreen versions of the portraits on the walls. Touch one and you can see more pictures of that person, audio recordings of their family’s remembrances, and an obituary. (The archive will grow over time as loved ones add more artifacts.) You can then choose to pro­ject or play those items in the inner room.

Impact Steel | These exterior columns bore the blow when flight 11 slammed into the north tower. Vincent Fournier

As you walk into the inner chamber, the perimeter is lined with benches facing inward. The floor is glass, and below your feet you can see the scarred bedrock that once supported the towers. The recorded material you selected plays across two opposite walls, which are covered in ultrasuede to ­muffle the sound and lend the room a hushed stillness. The entire space is designed for eye contact, like a Quaker meetinghouse: On the perimeter, you meet the gazes of the other visitors. The experience is communal—but also intimate.

It’s hard to miss the resemblance to the original memorial room at One Liberty Plaza overlooking Ground Zero. Just as that room had windows papered over with pictures and a ledger in the center for family remembrances, this new memorial has a perimeter of pictures and an inner chamber for displaying family recollections of the lost. Hennes says the similarity wasn’t strictly intentional, but he allows that the original memorial room may well have exerted an unconscious influence on him and his colleagues.

The solution they came up with, obvious as it may seem, obscures the parade of designs—many of them sophisticated and ingenious—discarded along the way. There were proposed skylights linked to the pools above, columns embedded with various media, an array of 2,977 lights. Each of these failed but also served a purpose. Through the whittling process, the designers found a solution that felt inevitable. That’s what remains. “It’s not very hard to be clever,” Barton says. “It’s far harder to be ­simple, obvious, and meaningful. It’s hard to make something feel like it needs to exist.”