On an August morning in Paris, when most of the city is in an advanced state of summer torpor, hundreds of young men and women are sweating it out in the third week of a gruelling month-long endurance test.
While the trial is called the "piscine" (swimming pool) and towels dot the ultra-modern building, the contest is not about physical prowess.
Welcome instead to the tryouts for Ecole 42, a free computer coding college founded by French telecoms billionaire Xavier Niel in 2013 to help young people find work in IT or, better still, become their own bosses.
Named after the offbeat answer to "the ultimate question of life" in Douglas Adam's comic classic "The Hitchhiker's Guide To The Galaxy," the ultra-modern college, with neither teachers nor conventional tuition, quickly gained cult status.
Around 40,000 people apply each year for one of roughly 1,000 spots on the programme.
Around 3,000 make it to the daunting "piscine" stage, in which the candidates spend 10 to 16 hours a day over four weeks completing projects and doing exams.
Some, like Aristide Rivet-Tissot, even sleep and shower on-site -- hence the towels.
"When you're here, you're so immersed that you sometimes forget the outside world exists!" the bleary-eyed 19-year-old told AFP as he greeted his parents, who had travelled up from the countryside to offer support and collect his washing.
- Dropouts welcome -
When Niel announced his plan for a free coding college open to all, including school dropouts -- 40 percent of the students do not have the school leavers' "baccalaureat" -- France's main IT employers federation gave a muted response, noting that the country already had an abundance of engineering colleges.
Six years later, Ecole 42, which is based entirely on project work and peer learning, has disproved the doubters with a 100 percent employment rate among graduates.
Describing a visit to 42 in Paris in a promotional video, Evan Spiegel, the CEO of social media giant Snap, declared: "You feel like you're walking into a school from the future!"
Now Niel, who founded the world's biggest start-up incubator in Paris in 2017, is taking his revolutionary model global.
After founding a Silicon Valley sister college in 2016, he has his sights set on Rio de Janeiro, Novosibirsk, Tokyo and a slew of other cities, as part of a plan to have 20 partner schools in 14 countries by 2020.
- 75,000 unfilled jobs -
A survey of businesses by France's unemployment administration last year found there were more than 75,000 vacancies in the IT sector.
While completing the course's 21 levels takes on average three years, many students are headhunted beforehand.
Bastien Botella, co-founder of Clevy, a start-up that develops chatbots, left 42 one-third of the way through the course to take a web design job.
A former hotel manager who failed his baccalaureat, Botella had previously been turned down by several traditional IT colleges.
"42 was a turning point in my life," said the 33-year-old, whose staff of 21 includes six fellow "42ers" working alongside graduates of some of France's top engineering colleges.
- 'School from the future' -
The school's inclusive approach marks it out in a country which preaches "liberty, equality, fraternity" but which was the worst performer among 36 countries, including the US and Britain, in a 2015 OECD study on social advancement through education.
Fadia Zementzali told AFP she applied after being fired from her job as a telephone saleswoman because she wears a Muslim headscarf.
"Here I was welcomed as a human being, not as a veiled woman," said the chatty 31-year-old, who was admitted to 42 in April.
The cross-community lure is plain to see in the kaleidoscope of faces clustered around gleaming 27-inch Apple screens in the vast computer room where the "piscine" trials are held.
"The digital sector, as we've seen at 42, acts as a social elevator. You have people from very different horizons," said 42 director Sophie Viger.
Despite not being certified by the state, the programme has won plaudits from politicians across the spectrum.
"It has brought innovation into our education system -- which is what we need and it's wonderful," then finance minister, now president, Emmanuel Macron gushed on Facebook after visiting the school in 2015.
But despite the glowing reports it has not been spared controversy.
In 2017, a French magazine reported allegations of sexual harassment and misogyny at the Paris facility, for which several students were punished.
Last year, France's digital privacy watchdog rapped it for "excessive video surveillance."
Viger said the school is working to attract more female students by promoting female tech role models and had complied with an order to remove most of its CCTV cameras.