in an unusual turn of events, it's people who are replacing computers at Klara Zenit, a massive building in the center of Stockholm. The 65,000-square-foot structure was a relic of the 1970s, designed to house the post office's old computer system. “It was a big black box without light in the middle,” says Yves Chantereau, an architect at Equator Stockholm, which gutted the building and carved out sunlit offices, retail shops, and rental apartments.

Downtown Stockholm is the epicenter of trendy restaurants, boutiques, and major department stores—prime real estate for retailers and condo development. But it lacked apartments for rent. To reduce the deficit, the city council asked Klara Zenit's developer to mix 100 modestly sized units with the new commercial spaces. Chantereau says the firm faced three big challenges: where to put the housing so as not to sacrifice lucrative retail space, how to break up the building's scale, and how to get light into the middle of the shoebox.

The architects produced a modern facade with brick tile and steel-and-glass, repeating and varying those materials to create different expressions. “We wanted people to read big scale so they would understand it's all the same building, but also be able to see small scale,” Chantereau says. Fifty apartments face interior light wells and a quiet street on the rear of the building; the other 50 are stacked on the roof and recessed, like a small village. The apartments are pitched not to an elite clientele but to singles and couples with modest budgets. With high-quality design ubiquitous in Sweden, the architects placed less emphasis on glamorous materials than on location. “We didn't put so much money into interior design,” Chantereau says. “What is exclusive is that you're in the middle of the city, like being on an island or in a penthouse.” No longer a cave for computers, the building now houses tech and media companies, including Sweden's largest daily newspaper, while increasing the opportunities for lively urban living.

The architects used steel, glass, and brick tiles to articulate Klara Zenit's massive facade in downtown Stockholm. Fifty apartments stacked on top of the building face interior light wells.

The architects used steel, glass, and brick tiles to articulate Klara Zenit's massive facade in downtown Stockholm. Fifty apartments stacked on top of the building face interior light wells.