Since its construction in the 1930s, the Vauban military base on the outskirts of Freiburg, Germany, has housed the Nazis, the French army and bands of squatting hippies and anarchists. These days, Vauban is home to a new crowd: environmentalists.

A decade ago, most of the barracks were torn down to make way for a sustain-able community that has become a sort of green utopia. Now, photovoltaic cells have replaced traditional roof tiles, bicycles outnumber cars and futuristic houses generate more energy than they consume.