The organisers promise something "spectacular" but their lips are sealed on the details. A handful of journalists, including Agence France-Presse reporters, were able to attend just a few minutes of a rehearsal this month.

Neon lights and disco balls contrasted with the industrial chaos of the decrepit but immense hangar. Such a huge space was necessary because, for the first time in Olympic history, the opening ceremony is not taking place in a stadium. Instead, it will stretch across seven kilometres of the River Seine with more than 3,000 dancers performing 10 different routines on the day.

"It requires real organisation, but we are doing it," enthuses choreographer Maud Le Pladec, in charge of dance for all Games ceremonies.

The organisation is millimetric, since the dancers must rehearse in small groups and the ceremony will have a dozen scenes.

Wearing a black tracksuit and sneakers of the same colour, the choreographer stands in front of her dancers. The rehearsal begins in good spirits, there is no time to waste. Le Pladec addresses them in English, she demonstrates the movements once, then a second, before giving them their turn.

The music resonates, unable to mask the noise of footsteps sliding over the floor— this passage of choreography is a mixture of relaxation and rigor. Shouts of encouragement echo as the movements are executed.

"We did it!" 

"Excellent, it makes you want to continue!" says the president of the organizing committee, Tony Estanguet, who has discreetly entered the room. A few meters away is also Thomas Jolly, the artistic director of the Games.

The opening ceremony will show "dance in all its diversity," reveals the choreographer. The goal, she confesses, is to achieve a crossover between "break dance", contemporary dance and classical dance.

"There won't be a bridge (in Paris) where there aren't dancers," she says.

No matter the style or the venue, for 25-year-old Louise Demay, dancing for the Games was a "childhood" dream that will come true. More pragmatically, Guilbeaud Manuarii, 19, confesses that she went to the auditions for "the pay", which "is not very high", she adds, when asked the amount. She admits to feeling a little nervous, but in tune with the "pretty sporty" choreography.

Will there be a more classical, ballet part? What will the suits be like? When will the general rehearsal be? To all these questions, the same response from the participants: "We can't say anything."

"Even the dancers don't know all the secrets," notes Le Pladec.

All feasibility tests have been carried out. Although it was necessary to readapt and change marginal elements, the initial project continues its course.

"Since mid-March, it has been coming together: the choreography, the costumes, the music... We did it!" She says.