In 1888, the French magnate Éduard Demanchy raised a mansion of imported European stone on the riverbank near Concordia and called it San Carlos. The Demanchys lived in it only three years, from 1888 to 1891, before moving on. Another French household, the Fuchs Valon family, took their place. Then came September 1938 and a fire that gutted the building, leaving the elegant walls open to the sky. What had been a showpiece of European ambition in the Argentine littoral became, in turn, a candle workshop, a fruit stand, and a salting house. The castle did not so much fall into ruin as drift through a series of humbler lives, each one a little further from the grandeur Demanchy had imagined.

In 1929, a Latécoère 25 mail plane developed engine trouble over the river plains. Its pilot was flying for the Aéropostale, threading the long, lonely routes that stitched Buenos Aires to Asunción del Paraguay, and he brought the failing aircraft down in the open ground beside the castle. The pilot was Antoine de Saint-Exupéry. Stranded, he was taken in by the family living in the half-ruined mansion with their menagerie and their unbothered snakes. He stayed long enough to remember it. Years later, marooned again in the Sahara after a real crash, Saint-Exupéry would draw on the experience of being a downed flier in the middle of nowhere for the book that made him immortal.

The legend is simple and beloved: that the two wild Fuchs Valon daughters, Edda and Susana, and their menagerie planted the seeds of "The Little Prince." There is no documentary proof, and most scholars trace the story's true origin to the desert crash. But the connection refuses to die. In 2019, the writers Nicolás Herzog and Lina Vargas published a book they called "The Little Princesses," tracing the legend of how the girls and their snakes and roses may have surfaced in Saint-Exupéry's imagination. A 2016 film, "Vuelo Nocturno" — Night Flight — borrowed the castle's romance directly. Whether or not the prince was truly conceived here, Concordia has decided that he was, and who can blame the city for keeping the story?

The household Saint-Exupéry stumbled into has become the heart of the legend. The Fuchs Valon daughters, Edda and Susana, were remembered as untamed blonde girls who roamed the grounds barefoot among a private zoo. Beyond the snakes under the dining floor, the family kept dogs and birds, a pet iguana, a mongoose, a fox, a monkey, and bees. To a French aviator passing through the South American backcountry, the scene must have felt like something out of a fable: a crumbling European castle on a tropical river, two feral princesses, and a houseful of animals treated as ordinary company. Whether or not it shaped a single line of his book, it is exactly the kind of place where one could imagine a small prince keeping a rose and taming a fox.

By the 1990s the castle was a scenic wreck, and the idea of saving it began circulating in agreement with the architect Magadán. Real work started in 2008, funded by the municipality of Concordia, the province of Entre Ríos, and the special fund tied to the nearby Salto Grande dam. In 2011 walkways were threaded through the ruins so visitors could move safely among the open arches. The restoration team won a prize for the best intervention of more than a thousand square meters, awarded by the International Conservation Center and the Central Society of Architects. The roof never came back. That was the point: San Carlos is preserved as a ruin, a romantic shell where the river light pours through empty windows.