TREIGNY — The place was an old quarry of ferruginous sandstone in a Burgundy forest 20 years ago. Now, the construction site of Guédelon castle, in central France, is packed with people and the parking lot is filled with a flock of buses. A crazy project at first glance, the construction of a fortified castle using 13th-century techniques has become one of France's major tourist attractions with about 300,000 visitors every year. The site is particularly popular among teachers, who see Guédelon as a golden opportunity to get their pupils interested in the Middle Ages. There are also older visitors, moved by the sight of blacksmiths and basket weavers working with ancient techniques, and numerous families.

Thirty-five people work on the site eight months out of the year, and 35 others assist them together with 600 volunteers nicknamed the "temporary builders." The latter, retired DIY enthusiasts or senior managers looking for a purpose, are allowed in at a rate of five days per season per person. Believe it or not, people are rushing to mix sand-and-lime mortar or to carry braided baskets filled with stones.

The entire economy of a fortified castle — blacksmiths, lumberjacks, carpenters, etc — is gathered on the 15-hectare site. The public loves the sight of two men walking like hamsters in huge wooden wheels. Their never-ending march drives a system of pulleys that transports the building stones. Farther in the distance, others are carving sandstone with a chisel — a movement that is said to hurt the elbows. The noise is relentless, regular. Carpenters are planing tree trunks for the framework without machines. "You need to have a trained eye and accept to work with the wood's irregularity," one of the craftspersons says. In total, the team will need to make 80,000 roof tiles by hand, which they will then bake at 1,000 °C in an oven (another one of the public's favorite attractions). By the river, they have built a hydraulic flour mill.

Everybody wears medieval-like clothing, giving the site a sort of hippie vibe. Only if you look carefully will you spot protective footwear, a concession made in the name of safety. "The work of craftspersons is a show, but we're the anti-Disneyland," says Maryline Martin, the project's director and co-founder with Michel Guyot, who owns several castles. Still, the workers are required to interact with visitors, who sometimes number 5,000 a day, and explain what they do — even in mind-numbing heat or when they're overwhelmed with work.

After 20 years of hard work and already a few years behind schedule, the castle's framework is ready, as are the great hall, two bedrooms, and a chapel. Two towers are about to be erected as well as a dovecote. Eventually, the fortified castle is supposed to resemble that of a lord's, a contemporary of Jean de Toucy and Crusader, who lived in the region in the early 13th century.

The castle was designed by a committee made up of several archeologists and one historian. Each decision — the size of the rib vaults, the decoration, etc — is a topic of discussion. "We study other medieval castles, like the ones in Dourdan and Ratilly," explains Florian Renucci, who's served as the project manager since its beginning. Other heritage sites, such as the Notre-Dame de Paris and Bourges Cathedral, have at some point seen "the people from Guédelon" turn up for an observation mission.

The last stone is expected to be laid in five years or more. Fundamentally, the timing is of little importance because the duration of the construction is also what constitutes its essence. Some visitors are regulars who want to see how the creation has evolved. There's even a "Guédelon generation" in the region that has grown up alongside the project.

Cultural heritage aficionados meanwhile have looked on the Guédelon castle with a mixture of allure and repulsion. At first, they kept their distance, especially given that at the beginning, even the people behind the project were largely dubious about how to go about with their plan. "There was a very Parisian sort of contempt," says Florian Renucci. "We haven't seen a lot of government ministers around here."

But Guédelon's recipe for success is now the stuff of dreams, and people are coming from far away to find out how the project has attracted so many visitors without having to harass the government or local representatives for a little help. Guédelon is an astounding economic war machine. The construction site got on its feet with the help of patrons. Twenty years later, it's financially self-sufficient thanks to its entry tickets (15 euros full price) and a well-stocked souvenir shop. Annual revenue is about 4 million euros. "We don't get any state aid, and we serve no master," says Maryline Martin. As far as culture is concerned, few sites can say the same.