This article originally appeared in the April 2012 issue of ELLE DECOR. For more stories from our archive, subscribe to ELLE DECOR All Access.Its only fitting that ELLE DECOR A-Lister Lorenzo Castillo happened upon the Madrid apartment building that would become his future home while en route to El Rastro, the citys famous flea market. Madrids old neighborhoods harbor hidden treasures, he says. Its one of the things I love most about the city. Simon UptonIn the sitting room, a steel-and-ostrich-egg mirror hangs above a sofa upholstered in a 1960s David Hicks fabric; the Jacob Frres armchair is covered in a Rubelli velvet, and the cocktail table is from the 70s. The artworks include paintings by Xavier Vilat, bottom left, and Jos Mara Yturralde, center, and a Josep Maria Subirachs engraving and Miguel Macaya painting, right.Castillo was immediately drawn to the building. Its very madrileo, he saysin other words, its quintessentially Madridwith a neoclassical stone faade that is noble in scale but remarkably simple. The portera, or doorwoman, told him the history of the building, which was constructed in the 17th century and was once a convent: Located on the border between the now-trendy neighborhoods of Lavapis and Barrio de las Letras, it became one of the most prestigious addresses in the Spanish capital during the 18th and 19th centuries. A new facade added in the 1770s by Ventura Rodrguez, the architect of many iconic monuments in Madridincluding the sculptures of Neptune and Cybele on the Paseo del Pradoheightened the buildings allure. Simon UptonAn 18th-century rug covers a table in the entrance hall; the bench is in the Rgence style, the desk is by Marc du Plantier, and 18th-century engravings fill the walls. Two days after Castillos first visit, a half-floor apartment on an upper story was his. That was 10 years ago, when he was building a reputation as a leading antiques dealer in Spain. Now he runs his own interior design business, with assistance from his partner, Alfonso Reyero. Castillos projects range from a historic Andalusian country house to a London restaurant slated to open this summer. He recently renovated Madrids Santo Mauro, giving the hotel a five-star upgrade. As Castillos business has grown, so have his domestic needs. Nearly four years ago he sold that first apartment, along with his collection of furniture and art, to purchase and renovate an 11,000-square-foot space downstairs, spread over two floors. Simon UptonThe center table in the drawing room was designed by Castillo, and the Louis XVI daybed is upholstered in a Josef Frank fabric; the 18th-century portrait is French, and the screen is Japanese. After the Spanish Civil War ended in 1939, the rooms that now house Castillos apartment served as the warehouse for one of the citys theatrical costumers. Such legendary figures as Maria Callas and Placido Domingo were fitted there for productions at the nearby Royal Opera House, Castillo says. By the time he bought the apartment, most of its signature architectural details were gone. The marble fireplace surrounds had been sold off or stolen during the war, and huge pieces of the decorative stucco moldings had crumbled or fallen off, he says. He spent a year supervising the renovation and traveling around Europe in search of period floors, fireplaces, fittings, and hardware. He became friends with the costume companys former owner, who could still conjure up memories of the apartments once-glorious appearance. Simon UptonThe armchairs, tables, and mirrors in the dining room are by Castillo, and the light fixtures are 19th century.Castillo managed to make the apartment look both classic and up-to-date. He wove a rich and sumptuous tapestry of timeless design by mixing pedigreed antiques and vintage pieces, including a desk of green leather and gilt bronze made in the 1940s by Marc du Plantier for the prince of Bavaria, tapestries by Rubens, a massive plaster bust from Pariss cole des Beaux-Arts, and 1970s Op Art. A carriageway behind the massive iron front doors leads to a glass-enclosed courtyard used as an indoor garden and decorated with chaises upholstered in a Madeleine Castaing fabric, the cast of a sculpture by Michelangelo, and an abstract painting by Lorenzos brother Santiago Castilloone of many throughout the house. A grand staircase, the type one expects to find in a Roman palazzo, ascends to a gallery where Castillo has continued the courtyards motif of plantings and black-and-white floor tiles. He cleverly deployed white trellis as a baseboard and as molding around the doors and balconies. Simon UptonA Louis XVI marble-top table and 1970s Italian chairs in the kitchen; the lacquer cabinetry is custom made, and the walls are painted in Farrow & Balls Lulworth Blue.Indeed, many of the room-defining elements are Castillos own subtle but beautifully executed designs, such as the coffered, mirrored panels that cover the walls of the glittering dining room, or the shimmering black-lacquer bookshelves with brass inlay that fill the library. A grand staircase, the type one expects to find in a Roman palazzo, ascends to a galleryThe upper floor is dominated by the 120-foot-long drawing room, the kind of space usually seen only in the backgrounds of princely portraits at the Prado. With five balconies and four seating areas, it is a sophisticatedand sometimes irreverentmix of periods, styles, and materials. French Second Empire, 19th-century Swedish, and 1950s Italian furniture share the stage with faded antique maps and crisp steel sculptures from the 70s. A massive hand-loomed carpet designed by Castillo provides the finishing touch.Simon UptonThe primary bedroom includes a tapestry by Rubens, a 17th-century octagonal mirror, and a 19th-century neo-Gothic dressing table; the wallpaper was designed by Castillo.Needless to say, such singular spaces make for fabulous parties. Castillo has hosted many, from intimate dinners to private couture fashion shows. But first and foremost, the home is where he and Reyero live and work every day. In the heat of summer well have lunch in the gallery, and on cold winter evenings we dine by candlelight in the mirrored dining room, he says. And since the home also serves as Castillos studio and showroom, he frequently slips into the guest suite to find a quiet place to concentrate. We truly live in the entire house, he declares proudly. Tour this former 17th-century convent in the heart of Madrid This story originally appeared in the April 2012 issue of ELLE DECOR. SUBSCRIBE