Photos show what the inside of the World Trade Centre looked like before it was torn down in a terror attack.
Most of us are now familiar with the horrifying images of the Twin Towers after they had been hit by hijacked planes, but less recognisable are the shots taken inside the buildings before the attacks.
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Footage filmed prior to 2001 shows the building packed out with people, taking photos and taking the lift up to the rooftop observation deck.
The World Trade Centre officially opened in 1973 and became a top tourist attraction, welcoming 200,000 visitors a day alongside the 50,000 people who worked in the buildings.
Tragically, the towers became one of the targets in a series of coordinated terrorist attacks on 11 September 2001.
Four airplanes were hijacked by Al-Qaeda suicide bombers, with one crashing into the Pentagon in Washington and another in a field in Shanksville, Pennsylvania.
The other two passenger jets were directed at the two towers of the World Trade Center in New York.
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The north tower was hit first, shortly followed by the south tower and in under two hours both 110-storey buildings had collapsed to the ground.
Almost 3,000 people died in the attacks, while more than 25,000 were left with injuries and long-term health problems.
Shockingly, the attacks could even be seen from space, with images from NASA showing smoke pouring out into the sky.
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Astronaut Frank Culbertson was the only American off the planet during the attacks, as he was situated inside the International Space Station with two Russian cosmonauts at the time, around 250 miles (400km) above Earth.
Culbertson spoke about the harrowing moment in the 2014 Astronauts: Houston We Have a Problem.
In the clip, he recalls: "I raced around and found a video camera and a window facing in the right direction.
"The weather was perfectly clear that day. I could easily see New York City - a big black column of smoke coming out of the city, and as I zoomed in with the video camera, I could see this big grey blob enveloping southern Manhattan.
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"What we were seeing was the second tower coming down."
In the clip, Frank can be heard telling Mission Control: "We can see New York City, and the smoke from the fires.
"Our prayers and thoughts go out to all the people there and everywhere else.
"Here I'm looking up and down the East Coast to see if I can see anything else."
Featured Image Credit: YouTube/Alessio Arigoni