Copenhagen’s ski hill has furnaces under its feet

You can ski down a working waste-to-energy plant in Copenhagen while rubbish burns inside it. CopenHill puts outdoor recreation on the roof of Amager Bakke, a facility that supplies electricity and district heating. Above the machinery, people ski, walk and take in the city. Below them, waste is processed for energy. This isn't a retired factory dressed up as a sports venue. The industrial job and the afternoon out occupy the same building, with a roof separating two very different ways to spend a day.

The slope owes its shape to what's underneath. Architects arranged the plant's machinery from tallest to shortest without sacrificing its efficiency, then used the resulting roof profile for skiing. Equipment that needed a huge enclosure helped create the height for a downhill run. The roof also carries planted areas and a hiking route, while a climbing wall runs up the exterior. Even the elevator makes the connection explicit: a glass wall faces the plant's interior, giving visitors a look at the machinery inside their artificial mountain. There's no attempt to pretend the factory isn't there.

The skiing works without a layer of snow because the surface is green plastic called Neveplast. Skis and snowboards travel over that artificial covering instead. But replacing snow changes the experience: skiers lubricate their skis on silicone mats before each descent to prevent frictional heat underneath. The surface also wears ski edges faster than snow does. The upper section is steeper, with gentler terrain farther down, so the roof accommodates different ability levels rather than offering one intimidating drop. Lifts carry riders uphill, and there are areas for slalom, freestyle skiing and children. It's a ski facility with a different surface, not simply a slanted lawn.

Inside, automatic grabs mix the incoming waste before feeding the furnaces. Mixing helps keep combustion steady. The unloading hall is held at lower pressure than the surrounding air to control odors, and its extracted air goes into the incinerators. Burning waste heats water in boiler pipes, producing high-pressure steam. That steam drives a turbine connected to an electricity generator. Heat remaining afterward warms water for the district heating network. After consumers use the heat, the water returns to be heated again. The plant gets electricity and useful heat from the same fuel.

Burning doesn't make the waste disappear. Ash and other noncombustible material remain, and the exhaust passes through filters, a catalyst and scrubbers to remove pollutants. Metals are recovered from the solid residue for recycling. The facility is intended for waste that can't be recycled; recycling materials is environmentally preferable to burning them for energy. CopenHill's cleverness is in putting a public recreation space above that complicated industrial process, not making the process unnecessary. You get a ski run upstairs. Downstairs, there's still serious work to do with what the city throws away.