Limburg’s Hidden Underground: 30 Years After Mines Closed
On September 30, 1992, the last Belgian coal miner emerged from the shaft in Heusden-Zolder, ending nearly a century of coal production in Belgium. More than three decades later, an investigation by VRT NWS has revealed that what lies beneath the Limburg soil is far more than empty tunnels—including abandoned locomotives, thousands of liters of chemicals, and an estimated 30 billion tons of unmined coal.
A Century of Coal
Between 1917 and 1992, seven mines operated across Belgian Limburg—Beringen, Eisden, Houthalen, Waterschei, Winterslag, Zolder, and Zwartberg—producing approximately 441 million tons of coal, about 32 percent of total Belgian production, according to Wikipedia. The mines formed an extensive underground network spanning hundreds of kilometers, with galleries up to five meters wide equipped with railway tracks. The mines of Zolder, Houthalen, and Beringen were even interconnected underground.
The human cost was staggering: an estimated 930 miners lost their lives in the Limburg mines.
What Was Left Behind
When the mines closed, operators recovered almost nothing from underground. The reason was purely economic—it cost more to bring machines to the surface than they were worth as scrap. This left a remarkable hidden world beneath Limburg.
According to former miner Eddy Pluymers, who now gives daily tours at the former mine site in Heusden-Zolder, brand-new locomotives were still being taken underground right up until closure. “The mines had contracts with suppliers and were therefore obliged to bring the ordered locomotives underground, even just before closure,” he told VRT NWS. “Those locomotives are still there, walled up in a large concrete bunker.”
Robert Coens, who worked 20 years in the Beringen mine, estimates that hundreds of kilometers of track, countless wagons, rail bikes, and 100 to 120 heavy metal frames per shaft were all abandoned underground.
A Hidden Environmental Concern
Perhaps more troubling than abandoned machinery is what else was left behind. “What is much worse are the thousands and thousands of liters of oil, grease, emulsion, chemical products, and asbestos,” Coens said. “That could all have contaminated the groundwater. At that depth, we’re really dealing with a small ecological disaster.”
Despite these concerns, the Flemish Environment Agency reports that the Vlaamse Milieumaatschappij does not conduct active research into possible contamination. The agency OVAM acknowledges materials were left underground but notes that above-ground spoil heaps were remediated in the 1980s.
The mines also left behind a massive cooling installation—1.5 meters wide and 20 to 25 meters long—that was walled into the galleries when the mines closed. Underground temperatures in Limburg rise 3 degrees Celsius per 100 meters of depth, reaching a theoretical 41 degrees at 1,015 meters.
Water Pressure Keeps Galleries Open
Contrary to popular belief, the underground galleries have not collapsed. After closure, mine operators stopped pumping groundwater, and the galleries filled with water. “That’s not true,” Pluymers said of the belief that everything collapsed. “A diver who explores abandoned mines told him that the water pressure actually keeps the galleries open. If we were to pump the water out again, you could in principle walk through them again.”
However, entering the shafts remains immensely dangerous. Coens explained that concrete dams were built around the shafts to prevent ground subsidence, and without maintenance, the spaces will eventually close themselves.
A New Future Above Ground
The mining legacy continues to shape Limburg’s present. The last remaining monumental shaft tower in Heusden-Zolder is currently being renovated, with completion now expected in autumn 2027 after rust damage caused a year-long delay, as VRT NWS reported. The tower will house the XR competence center De Skip and a skybar with panoramic views.
Meanwhile, the flooded mine galleries—which contain water up to 40 degrees Celsius at depths of 500 to 1,050 meters—offer potential for geothermal energy extraction, according to the Flemish government. The EU Methane Regulation (EU/2024/1787) now requires member states to map closed coal mines and monitor methane emissions, though Flanders’ fully flooded mines no longer emit methane.
The Wound That Never Closes
For former miners like Pluymers, the closure remains deeply personal. “I was never able to say goodbye to the underground,” he reflected. “It’s the wound that will never close. It becomes a scar, but one we are proud of.”
Standing at a manhole cover marking where tens of thousands of men once descended, Pluymers hopes for more recognition. “Many people don’t know that on exactly this spot, tens of thousands of men were swallowed up by the rich underground for decades,” he said. “Hundreds of them died. I sincerely hope there’s still a small budget left for a small monument, because our past deserves more than an ordinary manhole cover.”
As Limburg continues to transform its mining heritage into cultural sites and renewable energy opportunities, the hidden world beneath—with its locomotives, chemicals, and 30 billion tons of coal—remains a silent witness to a century of labor, sacrifice, and community.