If Raf Simons weren't the influential fashion designer behind Jil Sander and his own eponymous line, he'd like to be a ceramicist. "There's something so romantic about it," he says. "I think about the South of France, the nature of clay, working with your hands. Fashion is such an octopus. You're connected to so many people: suppliers, pattern makers, production teams, marketing teams, vendors. . . ." Six years ago, the 43-year-old Belgian went from being the under-the-radar, trend-driving menswear designer of Raf Simons to the top man at Jil Sander. With that coveted post, which includes overseeing men's and women's wear, has come much critical praise—particularly for exploring minimalism through proportion and color in women's wear—and countless opportunities. But Simons remains notoriously private. Quiet and sensitive, he lives alone in Antwerp, preferring the gentle lull of that city to the hardworking buzz of Milan, where he is obligated to spend almost 110 days a year for Jil Sander. He does not attend the high-flying black-tie affairs that are standard for so many of his peers. And he rarely allows himself to be photographed. "I'm not so rock and roll," he says, jokingly. "I'm more techno." In more ways than one, his art-filled apartment has become his sanctuary.

Designed in 1968—Simons thinks it's kismet that it's the year he was born—by a Belgian couple who imported Modernist furniture, the two-story, open-floor-plan apartment is a primer in mid-century Modernism. A longtime collector of mid-century furniture, Simons knew he would buy it the minute he saw the wenge-wood floating staircase, built-in cabinets and floor-to-ceiling sliding-glass windows. That it's located in Antwerp's heavily Orthodox Jewish neighborhood, far from the ritzy homes and shopping area near the city's central cathedral, didn't matter in the least. Nor did the creaky floorboards and outdated electrics. Simons, who purchased the apartment nearly six years ago, hasn't changed a thing. "It's perfect just the way it is," he says, sitting on a Pierre Chapo chair in a plaid button-down shirt and paint-splattered Alexander McQueen denim shorts. "I love the '50s and '60s; we were going to the moon; people were wondering what the world was going to be like; there was this idea about being surprised by the future." He's even learned to embrace some of the home's quirkier elements, such as five marble planters that randomly jut out of the entryway floor. (Finding plants that can survive in the low light has proved more difficult.)

Although lauded for exploring haute-couture concepts on the runway, Simons never attended fashion-design school. Instead, he studied industrial design at a small school in the Belgian city of Genk, specializing in furniture making. He gave it up, in part, because he found the manufacturing process too slow and isolating. But a quick glance around his minimalist apartment shows that furniture remains more than a passing interest. When it came to decorating, Simons did it all himself. There is a Pierre Jeanneret couch and chairs in the living room, upholstered in navy cotton with red piping. (The pieces were originally made in the '50s for public buildings in Chandigarh, India, the architecturally rich northern capital that was a popular testing ground for Modernist designers, such as Jeanneret and his cousin Le Corbusier.) Another set, in black cowhide, resides on the second-floor balcony. Upstairs, these are complemented by a low Chapo coffee table and Georges Jouve ashtray. A Ron Arad "Rolling Volume" chair serves as a bridge to the contemporary art on the walls. Downstairs, the Jeanneret is mixed with a Margot rug and various George Nakashima originals, including a conoid bench, woven lounge chair and rare dining-room table with five asymmetrical legs.

Casually sitting at the table, Simons doesn't mind that his glass of Diet Coke starts making a ring on the wood. "I spend a lot of time reading about artists, trying to figure out how they approached something. Where did it come from? Nakashima wanted his work to be lived in," he says. "When you have a house that's overly designed, it's so slick. I don't like that. I could never say, 'Watch out, don't sit on that.' "