To anyone who knows Carlos Martínez, Gensler principal and firmwide design leader in Chicago, it must have come as a surprise when he announced he'd be trading his Miesian high-rise lifestyle for the Gilded Age opulence of the Gold Coast. He and his partner, communications consultant Michael Tirrell, have been collecting art over the past 20 years-the kind of modern and contemporary work most often imagined in stripped-down, crisp white environs. The transition would call for back-to-square-one strategizing and the subtle manipulation of everything from the floor plan to the finishes.

In a bit of serendipity, Martínez once worked as a junior architect at Holabird & Root-known as Holabird & Roche back in 1897, when it completed the eight-story apartment house. The concept of vertical living was not very appealing at that time, especially to the socially registered residents of the mansions that anchored the nascently tony neighborhood. "I feel a kinship with the building's first occupants, who obviously were open to progressive ways of thinking about social and economic status. Chicago had just hosted the World's Columbian Exposition, and the mind-set was to move away from Victorian fuss in favor of a cleaner neoclassicism," he says. During his research on the building, he also discovered that modernist pioneer László Moholy-Nagy lived in this very apartment soon after moving from Germany to direct the New Bauhaus school. (Later, he founded what would become the Institute of Design at the Illinois Institute of Technology.)

There were decades of fusty upgrades to remove to get back to the 3,000-square-foot apartment's original interior, then decisions to be made as to how much of that interior could be altered with integrity. "Architecture is here to stay. Furniture and artwork are transient. It isn't a coincidence that the Spanish word for furniture, muebles, also means movable," Martínez explains. That said, he removed awkward walls to combine the servants' quarters and butler's pantry with the tiny kitchen. Most meals for the early residents were served from a communal kitchen, but people simply don't live in the same Upstairs Downstairs manner as they used to.

After the 19th-century floor plan was altered to accommodate 21st-century appetites, leaving heating lines and plumbing pipes exposed in the new kitchen, he transformed them into "columns" clad in crimson tile. And he concealed a shaft-facing window behind an ingenious frosted-glass box lined with dimmable halogen fixtures. "Since there wasn't any view, I designed one," he says. The view into the breakfast room, meanwhile, is dominated by a massive photograph of Julia Child-a souvenir of a memorial exhibition organized by Gensler. Formerly a maid's room, it can now morph into a comfortable guest suite, thanks to pocket doors, a Murphy bed, and a revamped bathroom.

The idea of defining a view dictated how all the art is hung. "I think of the picture moldings as frames focusing the eye on a painting," Martínez says. He restored the moldings, where needed, after removing the previous owner's floor-to-ceiling bookshelves. "Besides covering up beautiful original details, they made the rooms smaller," he explains­. Because ripping out the shelves unfortunately left a discolored lip running around the perimeter of the floor's quarter-sawn white-oak strips, he painstakingly refinished them with archival wax-more difficult to maintain but offering a depth impossible to achieve with synthetic products. That same previous owner had also installed an inordinate number of closets, and these have now been reduced. Martínez is no fan of closet doors either­, so he replaced most of them with weighty cotton velvet curtains. As he explains it, "Doors need so much clearance, whereas curtains are beautiful and economical." While absorbing sound and exuding richness, they free up wall space for the ubiquitous works of art. They're protected from damaging sunshine by UV film, applied to the windows, as well as by sheer white shades.

With the nearly three-year rehab now complete, the couple, their vizsla, Blue, and their collection have settled in with aplomb-and one significant addition, a remembrance of their previous high-rise home. Each hallway there was themed to a different artist, and they lived on the Gene Davis floor, so Tirrell surprised Martínez with a pair of Davis lithographs. "We walked by those striped prints constantly. I'd like to do a whole wall of them someday," Martínez says, scanning his already art-filled rooms for a place to make that happen.