Only a few years ago, cities were declaring their downtowns dead, victims of regional shopping malls, online retailers and suburban sprawl. But some urban shopping districts have come back big time. “They have what I call the X-Factor of Urbanism. Very cool, historic and filled with interesting shops and restaurants, surrounded with walkable neighborhoods,” says Robert Gibbs, an urban planner who has worked with 300 cities and teaches at Harvard’s Graduate School of Design. He says vacationers spend more time shopping than on any other vacation activity, making these neighborhoods natural for travelers.