Journalists were on Wednesday given unprecedented access during a tour around the inside of the 850-year-old World Heritage landmark.
Just three months ago, it would have been packed with worshippers and tourists admiring the Gothic architecture and famed stained-glass windows, which emerged largely unscathed from the inferno.
On Wednesday, instead of crowds, only a few dozen specialist workers wearing white protective overalls, hard hats and masks could be seen carrying out painstaking work to make the building safe.
Great protective nets have been hung to prevent objects falling from the roof and causing damage, and staff must guard against lead poisoning because of the contamination caused by the old melted roof.
An acrid smell still hangs in the air, while rows of untouched seats at the front of the cathedral are a reminder of what it looked like before the blaze, whose origins are still unknown.
The visit came a day after the French parliament finally passed a law on the reconstruction of the cathedral, which President Emmanuel Macron wants completed within the next five years.
The restoration work, which has not begun yet, will require replacing the roof, much of which was destroyed in the fire, and the spire, which collapsed to the ground.
'Nothing thrown away'
But before any of this can begin, the cathedral needs to be secured so that no part — in particular the vault — is at risk of collapse.
“We are not at all in the restoration (phase). We are still in the urgent securing” of the cathedral, said Notre-Dame's chief architect Philippe Villeneuve.
The risk of collapse is still so great that only remote-controlled machines are allowed to access some areas.
A large pile of rubble has been gathered in the middle of the nave and Villeneuve said every piece will be scrupulously examined.
Parts of a destroyed ribbed vault and scaffolding are seen during preliminary work.
“Nothing is thrown away,” he said, adding that analysis of each piece will help provide an ultra-precise scientific picture of the cathedral ahead of the restoration.
“The site is not just a place for architects but for scientists and researchers,” he said.
“A catastrophe took place, but it will bring a lot of new knowledge.”
Despite the damage, the great cathedral's grandeur remains, with its great pillars in the nave standing tall, its main organ intact and the great rosette stained glass window radiating colour in the summer sunshine.
Culture Minister Franck Riester, who like the journalists donned white overalls and a hard hat for the visit, hailed the progress but emphasised the long road ahead.
“There was a mountain of rubble there just a few weeks before,” he said.
Riester said the workers were wearing special masks because of the presence of lead which seeped into some of the stone during the fire.
“We need to take all the necessary measures,” the minister said.
He said the five-year deadline set by Macron was “not the question for today. The question is securing Notre-Dame”.
Paris prosecutors said in June that a poorly stubbed-out cigarette or an electrical fault could have started the fire and opened an investigation into criminal negligence, without targeting any individual.
On June 15, two months after the fire, clerics conducted the first mass inside the cathedral since the blaze, donning hard hats along with their robes for their safety.
French MPs on Tuesday approved a law on the reconstruction of Notre-Dame, three months after flames ravaged the great Paris cathedral, but did not address the controversial question of whether it will be rebuilt in a modern or traditional style.