A rusty winch slowly raises the elevator nearly 4,000 feet from the depths of the Tsentralna coal mine in Toretsk, a city of 67,000 people in the Donbas, an industrial region in eastern Ukraine.

As the giant cage reaches the top of the shaft, dozens of lights appear from the darkness, shining from helmets and flashlights as the miners, covered in black dust, step off and head to the showers, their workday finally over. On their way, they nod to their colleagues starting the day shift, who are waiting to make the descent.

During the Soviet era, the Donbas — short for Donetsk Basin — was a crucially important hub for heavy industry. Tens of thousands of people worked in the more than 200 coal mines that operated across the region.

The mines, once the beating heart of the region, where giant mountains of metal waste known as slag still dot the landscape, now represent a looming environmental catastrophe.