In a former industrial zone of downtown Toronto, more than 70,000 people—and counting—are now living in high-rise condo buildings. And where will they and their dogs hang out? Under an elevated expressway, thanks to the tentatively titled Project: Under Gardiner, a mile-long, 10-acre park that will open next year, driven by $25 million from private donors and an ambitious timeline. Urban designer Ken Greenberg and landscape architecture firm PUBLIC WORK envision a walking and cycling trail, performance spaces, markets, a cafe, an adventure playground, and a skating trail—all with staff "programmers" to engage locals and bring daily life to the place. "A new form of city is emerging on the traces of the old," Greenberg says. "This underused resource becomes a living room for the city."