We talk a lot – on this podcast, and on the website from which it spun off – about the practical side of cities: buildings and roads and railways and so on. But that's only half the story, of course. So this week, we're talking about the other half: shouldn't cities be fun, too? And what can we learn when we try to make them so? To discuss the joyful and spontaneous side of city life, I'm joined by Usman Haque, founding partner of the interactive architecture firm Umbrellium. He tells me about his experiences developing virtual pedestrian crossings, which can move about at will, and getting a thousand people to construct a temporary skyscraper in Singapore. We also discuss his favourite entries in this year's Playable Cities Awards, in which he was a judge. Skylines is the podcast from the New Statesman's cities site, CityMetric. It's hosted by Jonn Elledge.