Don't ask Marcus Robinson what he does and why he does it if you don't want shivers running up your spine. As day-time jobs go, this one takes some beating.
"The Twin Towers collapsing has become part of our collective consciousness. I felt that by capturing beautiful images of the transformation, it would be possible to tell a powerful story of light emerging out of darkness and destruction," he said.
"It's a story of epic architecture and engineering, but also about the amazing construction workers doing the rebuilding. Healing a scar..."
A poignant, touching mission statement from a man with a rather special mission.
For Marcus Robinson, this is a once-in-a-lifetime calling, a priceless opportunity to be at the heart of the biggest, and most emotionally driven, rebuilding programme in history.
You listen to the 53-year-old Northern Ireland man's words on the acclaimed new documentary he has written and directed, and suddenly you're propelled back to this date 12 years ago.
To a never-to-be forgotten day of screams, horror, panic, confusion and wailing sirens as iconic American landmarks collapsed before unbelieving eyes.
A day of unadulterated terror when evil came calling, leaving with nearly 3,000 dead and millions of others terrified and traumatised.
But out of the dust and ashes of what New Yorkers simply refer to as "that day", the World Trade Center is rising again; stronger, taller, better.
It has taken 12 fraught years and more than $15bn (£9.5bn), but the Big Apple once again boasts the tallest building (One World Trade Center) in the western hemisphere, its 1,776ft height a deliberate nod to the year of a nation's birth; a symbol of defiance, optimism and hope.
And Marcus, born and reared in the hills above Belfast, is the man tasked with recording that phenomenal transformation from the haunting images of Ground Zero to the most breathtaking 16 acres of real estate the planet has ever seen.
The artist, architectural photographer and film-maker has spent six years visually documenting a project that will probably last at least six more, and will ultimately produce six jaw-dropping skyscrapers, a heartrending memorial and a gargantuan transportation hub around the area where the Twin Towers stood until "that day" in September 2001.
Using the time-lapse photography, sketches and paintings that were recently showcased in his Channel 4 documentary "Rebuilding the World Trade Center", Marcus is busy producing a unique portfolio of striking, powerful and beautiful images, a breathtakingly vivid history lesson of the future.
And yet, technically, it's not even a job. No-one asked the former Campbell College student to do this – and no-one's paying him.
He's financing it himself – but this is a man who once worked as a domestic cleaner just to make ends meet, so his resourcefulness is not in question.
"I just knew in my heart that this was something I really, really wanted to do," he said.
"It's like being guided by a voice, when you believe what your heart is telling you to do."
Marcus's heart spoke to him on February 27, 2003 – the day world-famous architect Daniel Libeskind was awarded the masterplan for the reconstruction of the WTC.
"I was in London when that announcement was made and something just bubbled up inside me," says Marcus who, with rather fatalistic irony, had been recording a major demolition project on the day the towers fell.
But it would take a further four and a half years of frustration, setbacks, security issues – and downright refusals – before a man on the phone finally said yes. Talk about time lapse...
And, with typical artistic surrealism, Marcus had been sitting in a lavender field when that call came.
"I had a dream but, like all dreams, it started with nothing," he says. "I mean, where do you start with something like this; who do you call on the phone?"
Fortunately, the first person he called, Daniel Libeskind's wife Nina, loved the idea and invited Marcus and two producers, who had been planning to raise funds for the project, over to New York.
Mrs Libeskind was enthusiastic and receptive, and put Marcus in touch with some influential people, but time moved on.
Money wasn't forthcoming, doors weren't opening – and his two disillusioned colleagues walked away.
"I was very naive back then," he admits.
"I thought people would say 'that's a great idea, here's a few hundred thousand dollars', but it was never like that."
He adds: "All I had was my determination and my vision – through years of transatlantic trips, goodwill, relationship building, patient diplomacy and negotiation – and trying to prove that, although I was London-based, I was fully committed to the idea."
Finally, in 2006, the movers and shakers behind the WTC – the Port Authority and real estate giants Silverstein Properties – gave him access to the site, just as the final debris from Ground Zero was being cleared away in lower Manhattan.
"I'd all but given up by that stage," admits Marcus.
"I was sitting painting in a lavender field near Grignan in France, where a friend of mine lives. The phone rang; I packed up immediately."
He won't forget his first day on site either: "It felt extraordinary. I was taken down to where they'd just started digging the foundations and seeing this incredible, beautiful bedrock that had been laid bare.
"It was as if someone had exposed the very soul of New York; this three-million-year-old rock that allows the city to look the way it does today."
The mesmerising images used in the Channel 4 film were created by 13 digital still cameras strategically placed around the site that have taken a picture every 30 minutes for the last six years.
They enabled months of frantic and complex construction work to be distilled into seconds, highlighting both the enormity of the task and the clockwork-like beauty of it.
The high point of Marcus's film, literally, was the intricate mounting of the huge metal spire that topped off One World Trade Center, with all the symbolism and emotion that went along with it.
But the Ulsterman is an artist who believes words are as important as pictures. In the documentary he interviews surveyors, engineers and the blue collar workers; those hitherto ant-like creatures in the delirious time lapse sequences.
"I wanted to make something that shows how camaraderie and togetherness can create something amazing out of nothingness," he says.
"Over time, a lot of the workers have become close friends. It's very humbling for me. I've been totally motivated by their passion, their belief in what they are doing.
"I see up close the incredibly hostile conditions they're working in. In winter it can be minus 20, while in the summer the heat can be absolutely unbearable."
No-one on site, least of all Marcus, is unaware that this place is also a mass grave, hallowed ground where 2,753 innocent people lost their lives. Like everyone else, he remembers where he was when the planes hit.
"I was making a film in Wales about the demolition at a power station when I heard the news. I found it impossible to believe that sort of thing could even happen," he says.
"There are no words that can adequately describe the horror, the scope of what happened. And it was captured on images beamed all around the world. Those images are beyond surreal, beyond apocalyptic."
He adds: "Because of 9/11 being a turning point in history, it has taken on quite dark, negative connotations. That's why I'm focusing on something really more positive, more uplifting."
It is no surprise that Marcus has painting, photography – and construction – in his DNA.
His late father Norman, who worked in the Harland & Wolff drawing office in the Forties, was a keen amateur photographer and painter.
"He was a real inspiration to me on every level," says Marcus, who was born on November 19, 1959, shortly after his parents returned to Northern Ireland from Canada, where his father designed ships for 11 years.
The family settled in the little Co Down village of Ballymiscaw and within two years his mother Eileen gave birth to Marcus's younger sister, Sherry.
"Those were happy days," recalls Marcus.
"My father got involved with my uncle in the family construction business and I grew up around building work and the materials of construction; I suppose that informed my own artistic sensitivity."
His mother, a gifted singer who performed at the Ulster Hall and in BBC recitals, had a keen interest in languages and this undoubtedly influenced the young Marcus to study French and German at Cambridge after his formulative years at Strandtown Primary and Campbell College.
But he never wanted a career in languages – although his French proved more than useful after he decamped to Paris, having sold his prized drum kit to finance the move to what was then his dream city.
"I was working as an English teacher, and cleaning staircases; doing all sorts trying to make a bit of money," he says.
"I got my break as a photographer in 1987 after a businessman saw some pictures I'd taken of Parisian suburbs and became my first client."
For the next 13 years Marcus worked for many leading architectural photography magazines, produced exhibitions, short films and books about his work, which included Paris landmarks such as the Grande Arche and the Pyramide du Louvre.
Then came a major opportunity across the English Channel – the London Eye.
"I moved to London after 16 years in Paris, and the Eye project ('The Millennium Wheel') was my first film – shot on a little super 16mm camera I'd brought with me from France," he says proudly.
It was his time lapse work on the London Eye that ultimately opened American eyes to Marcus's work, and an apartment in Manhattan – overlooking the site, of course – has been home for the past seven years.
Next month the Big Apple will host his wedding, to the 30-year-old New Zealand fashion designer Lucie Boshier.
"I've always loved New York, always been inspired by the spirit and energy of the place," he says.
"A terrible thing happened here 12 years ago. But now, hopefully, I'm giving back a slightly different vision of September 11, 2001."