OF all the neighborhoods that lie along Seattle’s Lake Union, the industrial district known as South Lake Union seems to have languished the longest. With nothing but boat and auto retailers, modest homes and takeout joints, few visitors ventured there, except perhaps to shop at the flagship REI store.

But that’s changing, thanks in part to the Microsoft co-founder Paul Allen.

The upgrade wasn’t easy. During the 1990s, local leaders tried to build something called Seattle Commons, an 80-acre park in the middle of South Lake Union, as a development anchor. But city voters rejected the plan in 1995 and 1996 as too costly, among other reasons.

Following the failed vote, Mr. Allen wound up with approximately 10 acres. Instead of letting the area lie fallow, his company, Vulcan, ultimately amassed 60 acres in a private push to convert South Lake Union into a biotech and residential hub  a kind of city within a city.

Five years later, the vision of a new South Lake Union is finally taking shape  from a drive-by no-man’s-land to a high-tech community dotted with gleaming office towers, cafes, a new farmers’ market and a lakefront park.