New York’s Long Island, a short drive from Manhattan, is an un-likely trove of modernist architecture. Audacious homes by mid-century luminaries like Richard Neutra and Frank Lloyd Wright pepper the island. But the modernist gem with one of the flashiest backstories may be the one with the least remarkable exterior: a barn.

The story begins in 1930, when New York socialite Mary Callery left her old life—including her husband and young daughter—and sailed to Paris to open a sculpture atelier. The daughter of a wealthy couple, she probably wasn’t living as rough as many of her fellow expatriate artists and writers had done in the preceding decade. But the fact that she came from money didn’t preclude her from captivating the Paris avant-garde.

This cosmopolitan cohort, members of the so-called Lost Generation, quickly adopted the sculptor and model into their milieu. Callery later rapturously described these heady Paris days, “when life looked beauti-ful, quivering with dreams of the mind.” Man Ray photographed and sketched her; Alexander Calder gifted her a brooch with her initials. In 1938, Pablo Picasso sketched a striking portrait of her head, oblique from behind, with à la mode rolled curls at the nape of her shapely neck.

Callery’s friendship with Picasso would open doors for her when she fled Paris as the Nazis took over in 1940. When she arrived back in New York, she was in possession of more Picasso works than anyone else in the United States.

Her salad days in Paris, her moveable feast, were over by then —although she would continue to return to Paris for short visits. But her time there informed the rest of her life, personally and professionally. Her primary artistic preoccupation remained sculpture. But given the nature of her work—hard materials like bronze and steel swirling and softly interwoven—it’s little surprise she felt a personal and professional affinity with architects. Her best-known work was commissioned by Wallace Harrison, the architect responsible for New York’s Lincoln Center and the Metropolitan Opera House. To this day, it hangs on the proscenium arch of the opera. Even if you’ve never seen it, it’s possible to deduce that the piece is abstract given its affectionate nickname: “Spaghetti Spoon in Congress with Plumbers Strap.”

Shortly after returning to New York, Callery embarked on a romantic affair with the German-American architect Ludwig Mies van der Rohe. Mies, as he’s known, had been the last director of the Bauhaus, the seminal school of modern architecture forced to close by the Nazi party in 1933. Among the fruits of their relationship was the barn he renovated in Huntington, on Long Island’s North Shore.

From the outside, the barn is wholly unexceptional—it looks exactly as quotidian as its name implies. This was by design. Mies was struck by the original bones of the barn, and wanted to retain its austere integrity. He did, how-ever, pick up the whole thing by its foundation and move it—to give those inside a better view of Long Island Sound.

Inside, Mies kept the structural beams in their original dark wood color, filling in the spaces in between with basic fiberboard painted white. The effect is similar to Heian-era Japanese interior architecture—white panels set off by long black lines— a famous fascination of the Bauhaus. It was a fitting neutral backdrop to Callery’s ever-burgeoning art collection. She amassed it under the name Mrs. Meric Callery to imply that there was a husband in the picture, which, after her second divorce in 1936, there wasn’t.

Today, Callery is better known for her collector’s eye than her sculpture, and the barn is not open to the public. Like Callery herself, it’s keeping its secrets.