Werner and Jutta's father died in Pit 9, which is the largest of the coal pits in Zollverein.
Zollverein is a coal-mining settlement outside of Essen, Germany. It's three hundred miles to the northeast of Paris. It's there, in the largest mine, that their father died and left them orphaned.
Werner sometimes takes Jutta there to watch the men work and the coal elevator run. When they're done with lessons, he walks there and pulls a cart that she sits in. He made it himself from abandoned pieces. They play all over the mining area, even climbing up on old machinery. Then they watch the bright lights coming from Pit Nine as the men enter it with their lunch pails, and he reminds her that inside the mine is where their father died.