In the Dordogne village of Montignac sur Vézère, the story of how one boy and his dog discovered one of the most haunting examples of prehistoric art has gone down in local folklore.

On 8 September 1940, Marcel Ravidat’s black-and-white mongrel, Robot, dived into a hole in the ground in pursuit of a rabbit. The 17-year-old Ravidat retrieved his pet, and returned a few days later with three friends to explore what appeared to be an underground cave. Dropping into the rocks, they entered a grotto where the flickering light of their oil lamp lit upon a painting of a red bull. The rest is prehistory.

Ravidat and his friends had stumbled across what became known as Lascaux, an extraordinary network of subterranean caves decorated with drawings and engravings dating back 22,000 years to the palaeolithic era.

The depictions of horses, bulls, bison, goats, deer, cows, as well as lions, a bear, a rhinoceros and even a unicorn were so strikingly beautiful that the local abbot, a historian, declared the grotto was a “prehistoric Sistine chapel”.

Some of the paintings in the Lascaux caves. Photograph: Denis Nidos/Département 24

Today, Lascaux is closed to the public and has been for more than 50 years, after it was discovered visitors were unwittingly destroying the Unesco world heritage site simply by breathing in the caves. But next week, French president François Hollande is expected to open a meticulous €57m (£48m) replica of the grotto that attempts to recreate the magic and detail of the original.

Germinal Peiro, the local MP, said it was the first time such an ambitious project had been attempted. “Lascaux is chez nous, but it doesn’t belong to us and we have always wanted to share these spectacular paintings with the world. This is the first copy of a grotto of this size in the world and it is a work of art in itself,” Peiro told the Observer during a pre-opening tour of the project, known as Lascaux-4.

An exhibition space in Lascaux 4. Photograph: © Casson Mann

Stepping into the replica grotto, built 800 metres down the hill from the original with the same sombre, humid atmosphere, visitors are greeted with paintings of herds of animals, overlaid on earlier older paintings or etched into stone, that have taken a dedicated team of modellers, sculptors and artists three years to reproduce, as near to the Cro-Magnon original as possible.

Archaeologist Jean-Pierre Chadelle described it as a work of art in itself and said work on the replica had enabled experts to discover new details about the original Lascaux, which he admitted had still not given up all its secrets. “We know the paintings were done with natural colours found in the earth around here, but we cannot exactly date the pigment so we cannot exactly date the paintings,” he said. “Lascaux is still a mystery, even today.”

He added: “We also know the paintings were done by tribes of hunter-gatherers, but there is no moon, no sun, no depictions of the countryside, or even pictures of reindeer, which we know they depended on for food.”

Chadelle points out that there is also only one semi-human figure: a naive stick figure drawn in black, with four fingers, and the head of a bird, who is either dead or injured. “Is this a man? We don’t know for sure. What we do know, given the time and effort involved in making them, is that the paintings represented something very important to the people of the time.”

Experts believe the Lascaux caves were not used as shelter but were more likely a spiritual sanctuary. The drawings, they say, were almost certainly created by skilled tribal painters, as opposed to the prehistoric equivalent of roaming graffiti artists.

In the excitement following the discovery of the Lascaux grotto in 1940, little heed was paid to the long-term conservation of the paintings. Workmen blasted through the hole in the rocks Ravidat and his friends had entered, to bring electricity and air filtration. Without a second thought, they lowered the floor to make a passage for visitors. Inevitably, they upset the delicate natural balance of the atmosphere within.

Between 1948 and 1963, when the caves were open to the public, thousands of visitors traipsed through the grotto. They brought with them bacteria, as well as moisture and carbon dioxide in the air they exhaled, setting off a biological chain reaction that caused fungus to spread across the paintings. First came the “green malady”, then the “white malady”, then “black stains”. The original grotto is being left to “rest” to find a natural balance. Only a handful of scientists are allowed inside to check on its health, and only with special permission.

The experts at work in Lascaux. Photograph: Denis Nidos/Département 24

Nicolas St-Cyr, artistic decorator of Lascaux-4, officially known as the International Centre for Cave Paintings, is one of the few to have visited the real Lascaux. “It’s very special. You have the feeling you are in the presence of man 22,000 years ago when you see the paintings. These were talented artists, working by the light of animal oil lamps, and it’s like they were done yesterday. I was trembling when I came out.”

A partial copy of the original grotto – Lascaux-2 – was opened in 1983 and has attracted 8 million visitors, and a travelling exhibition – Lascaux-3 – is currently touring Asia. Lascaux-4, which has received funding from regional and department authorities, the French state, the EU and public donations, is expected to attract 400,000 visitors a year. Award-winning London design company Casson Mann was responsible for creating the exhibition space, which includes a cinema, an interactive picture gallery and a theatre.

St-Cyr added: “It’s impossible for anyone to see the original now, but this is the next best thing. What is lost in not having the real thing is balanced by the fact people can see so much more of the detail of the wonderful paintings and engravings.”