This summer, British designer Thomas Heatherwick breaks ground on not one, but two projects that reimagine what urban parks can be: Manhattan’s Pier 55, a nearly three-acre oasis to perch atop concrete columns on the Hudson, and Garden Bridge, a lush 1,200-foot-long expanse to connect the banks of the River Thames. Pier 55 will offer a wooded offshore park complete with performance spaces, while London’s Garden Bridge will be a pedestrian crossing dotted with planted vignettes; clad in a copper-nickel alloy "skin," it promises 120 maintenance-free years. But ultimately, these projects demonstrate how divisive public works can be. Both have undergone political scrutiny, with questions raised about economic and environmental sustainability and the sheer cost of each park—a projected $130 million for the pier and £175 million (about $250 million) for the bridge. They’re slated for completion in 2019 and 2018, respectively.