Copenhagen is already home to large tracts of open space, as well as 242.3 miles (390 kilometers) of bike lanes, which one in three residents uses to commute to work or school every day [source: City of Copenhagen]. With 60,000 residents expected to join the population by 2025 and designs on becoming the world's first carbon-neutral city by the same year, the Danish capital, which was among the first municipalities to offer incentives for environmentally friendly practices, continues to be home to key advances in green construction [source: City of Copenhagen].
The country's building regulations state that by 2020, buildings' energy consumption must be less than 30.7 kilowatts per square meter per year [source: Danish Architecture Centre]. In 2010, city officials mandated that all new and old rooftops angled under 30 degrees must be green -- meaning that they are literally covered with vegetation to absorb rainwater and cool the building, among other benefits [source: Nusca]. One of the most intriguing projects is expected to open in 2016: a new municipal waste incinerator that will generate energy to power tens of thousands of neighboring homes and feature a ski slope running along its exterior [source: Witkin].