LOOKING up at the World Trade Center, I could barely see where the two towers ended. They disappeared into the clouds, making surrounding skyscrapers look oddly mediocre.

Our New York city break schedule left no time for the North Tower’s 107th floor and its Windows on the World view - we’d booked the Empire State Building that day instead. “Next time!” we said, taking one last look at those gigantic towers.

Six months later, on September 11, 2001, they collapsed into the ground, covering much of the city in a suffocating post-apocalyptic fog.

The following year I returned to New York. It was eight months since two hijacked airliners had taken nearly 3,000 lives and the grief was still raw. I wasn’t sure about going to Ground Zero. I’d heard there was a viewing platform and souvenir stalls. It felt tacky, and intrusive. But alongside the grief was a sense of defiance in New York, where Stars and Stripes flags hung from every other window. “Have you been yet?” someone asked us in a bar a few blocks from Ground Zero. “You should go.”

New Yorkers were wearing their hearts on their sleeve, and we were expected to pay respects. So we walked to that grim place where the Twin Towers had stood, and as we approached the shrine of photographs and handwritten cards, the bustle of Lower Manhattan’s financial district was smothered by an eerie quiet. There was just birdsong and the methodical clanking of cranes from the ongoing clear-up operation behind a steel wall.

We joined other tourists shuffling past railings, now a wall of remembrance, leaning in to read some of the unbearably sad messages to people who went to work that September morning and didn’t come home. The cards and letters had smudged and faded over time, along with photographs of the missing, and pictures of firefighters drawn by schoolchildren, pinned up next to frayed NYPD T-shirts, bandanas and flags. At the foot of the wall was an assortment of fire helmets, candles and dying flowers. Nearby, young men were selling ‘I Love NYC’ trinkets and Twin Towers postcards from open suitcases. It felt strangely appropriate, and reassuring, to see that in the shadow of those awful twisted steel girders, New Yorkers were continuing to make a fast buck. In the midst of so much grief, chaos and loss, a steely-eyed defiance burned bright in a city built on hard graft.

More than a decade later, I was back in that place, this time gazing into a deep shimmering pool. The cards, T-shirts and candles had long gone. The ‘footprints’ of those two enormous towers had been turned into twin reflecting pools, with waterfalls, surrounded by parapets engraved with the names of the men, women and children killed in the attacks of September 11, 2001.

The 9/11 Memorial is a place to reflect and remember, and its museum re-visits the events of that day, the aftermath and the conflict, soul-searching and re-building of the following years.

All around it, the daily bustle and noise of Lower Manhattan continues. Sharp-suited men and women grab bagels-to-go from street corner delis and guys in NYC baseball caps flog tourist tat from suitcases. The air is filled with the familiar honking of yellow cabs. Twenty years on from a day that changed it forever, New York continues to be a city that never sleeps.

l Were you in New York on September 11, 2001? Were you or your family involved in the events or clear-up operation? Email emma.clayton@nqyne.co.uk