The 2,583-square-foot unit, located in the upmarket L’Eixample area of Barcelona, sported original Art Nouveau details: richly ornamented plasterwork, floor-to-ceiling windows with wooden shutters and brass hinges, and porcelain handles on the doors. A long hallway, lit on three sides by colorful stained-glass windows, connected the rooms at the front of the apartment with the library and the adjoining conservatory at the rear. Gray, brown, and white tiles, arranged to form delicate flower patterns, covered the floors in every room. “That’s really very unusual,” says Vila D’Acosta-Calheiros. “In old Catalan apartments, you normally find different tiles and patterns in each room. The uniformity of the tiles and patterns here imparts a sense of calm and space. Everything was just so perfect.”

One of Spain’s best-known interior designers, Vila D’Acosta-Calheiros founded the Minim design studio and showroom with Agnès Blanch Vallès in 1999. The pair specializes in integrating furniture and accessories into rooms in such a way that the spaces remain light and breezy. “Respecting the location is a part of our philosophy,” explains Vila D’Acosta-Calheiros, who was born in Cuba and studied architectural restoration in Mexico. She took the same approach for her own home. “I let my surroundings speak,” she says, “and I listened carefully to what they had to say.” To her, it was clear: The old rooms should remain as untouched as possible.

In 1910, when the building was constructed, Barcelona’s economy was booming and, as a result, so were the arts. Architecture was especially popular among the city’s wealthier citizens, and splendid buildings were built in the new neighborhood of L’Eixample, on the edge of the old, Gothic city center. Modernismo, which later became known as Catalan Art Nouveau, was the preferred architectural style in the upper echelons of society, and Antoni Gaudí was its most famous exponent. Some of the buildings he designed, such as the Casa Batlló and the Casa Milà, are just around the corner from the couple’s apartment. Their town house, designed by the little-known architect Telmo Fernandez, has the sumptuous, almost excessively embellished facades and richly decorated interiors representative of this era.

The couple had some basic work done on their new home, including painting the windows and door frames and cleaning the stucco and floor tiles. To better accommodate their family, they made a few strategic structural changes, such as moving the kitchen from the center of the apartment to one of the bigger, airier rooms at the front and removing a wall to better connect the new kitchen to the living and dining rooms. “There are four of us in the family,” notes Vila D’Acosta-Calheiros. “An apartment must not only be beautiful, it must also be practical.” This group of rooms now forms the focal point of family life. The former kitchen was converted into two bathrooms, which are situated next to the bedroom of their 15-year-old daughter, Luna. Their 22-year-old son, Pablo, has moved into a room on the floor above—in former servants’ quarters, reached via a narrow staircase. He has declared this part of the apartment a “design-free area.”

In the other rooms, midcentury classics, like dining chairs by Hans Wegner, share space with contemporary objects, such as lamps by Marcel Wanders, a sofa by Piero Lissoni, and stools by Jasper Morrison. At work, Vila D’Acosta-Calheiros’s and Gorriz’s roles are strictly separated: He looks after the business side of the firm, while she does the interior design work. However, they planned their home together. “We wanted to create a modern contrast to the original structure of the building,” says Gorriz. “As the apartment already boasted a wealth of original details, we decided to use restrained colors and natural materials, such as cloth, iron, and wood.” The furniture combines high quality with functionality. There are, however, a few exceptions—such as the three white chairs by Junya Ishigami, which are more eye-catching than comfortable. “We couldn’t resist them. They’re simply too beautiful,” says Vila D’Acosta-Calheiros.

Although the couple originally planned not to hang any art, they did mount a large-format photo by Jordi Bernadó in the living room. “It has so much depth,” says Gorriz. And behind the dining table, a work in wood by a Cuban artist friend, Maria Sanchez, breaks the austere white of the walls. “But we’ll probably leave it at that,” says Vila D’Acosta-Calheiros, who doesn’t want too much art and design to distract from the real protagonist: the enchanting beauty of the old rooms.