For places that were meant to be unseen, alleys take up a not-insubstantial amount of space. A 2011 report by Mary Fialko and Jennifer Hampton, graduate students at the University of Washington*, found that in Seattle, there are 217,000 square feet of public alley space downtown, 85 percent of which are underused. The report estimated that reinvigorating alleyways could increase the number of total public space in the city by 50 percent.Alleys, too, are vital players in a city’s overall ecosystem. As the need for cities to rely on more sustainable approaches has become more pressing, the proliferation of trash and flooding in alleyways has come to be seen not only an aesthetic blight, but an environmental one.And as Daniel Freedman of the Los Angeles Sustainability Collaborative says, there’s a lot of crossover between sound environmental practices and livability. Revitalizing an alleyway creates an opportunity to introduce green infrastructure, but also, Freedman says, it invites the surrounding community to collaborate on improvements and make use of the space.