This city ski slope heats and powers 150,000 people—by burning their trash. It sits on top of Copenhagen’s waste-to-energy plant, CopenHill. In the late 2000s, the city wanted to shut down coal but still had 440,000 tons of non-recyclable waste to deal with every year. Instead of burying or exporting it, they turned it into energy. The challenge: build an incinerator that’s clean, efficient, and embraced by locals. Danish architects BIG—Bjarke Ingels Group proposed something radical: make i...