Riemst (Brussels Morning Newspaper) – The marl caves in Riemst face vandalism and waste. About 20 volunteers joined a cleanup in the Ternaaien-Beneden quarry. Mayor Mark Vos seeks to close the remaining Walloon entrances.
As VRT News reported, the marl caves in Riemst, in the province of Limburg, Belgium, are facing growing problems from unwanted visitors. The Ternaaien-Beneden marl quarry on the Castert plateau is popular with urban explorers and adventurers.
Officials mentioned that these visitors leave behind large amounts of trash. While litter can be cleared during organised cleanups, the problem is graffiti. The white limestone walls are being damaged. Spray paint and carvings cover the historic surfaces.
“Unfortunately, there are still places where people can enter the caves,”
Says Suzanne Hanssen of the Subterranean Limestone Quarries Study Group.
What threatens Riemst’s Marl caves despite the Volunteer cleanup?
A major cleanup is underway today, Sep 27, 2025, by the Study Group for Subterranean Limestone Quarries. Volunteers are carefully removing waste while protecting the limestone walls. Experts warn that if vandalism continues, future generations may not see the caves in their original state.
“More caves on the Walloon side must be closed.”
Mark Vos, mayor of Riemst (CD&V)
Many entrances to the marl caves in Limburg have been closed in recent years. However, several access points remain open, especially on the Walloon side. People continue to enter the quarries illegally. Mayor Mark Vos has said he wants to close these remaining entrances as well. Entering the caves is against the law and remains dangerous.
“The cave that is being cleared today is located on Flemish, Walloon and Dutch territory,”
Says the mayor.
Around 20 volunteers spent the entire day cleaning up waste left behind by visitors. They worked to remove litter and debris scattered throughout the quarry. Officials stress that cooperation between regional authorities and local communities is necessary.
The underground marl caves known as Riemst, including the Ternaaien-Beneden quarry located on the Castert plateau, have been in existence since the 15th century. The underground quarries produced Maastricht Stone, which is a locally occurring, soft, and porous limestone.
Quarrying for stone started in the 15th century and continued into the 20th century, with some locations still being quarried within the past few years. Over the years, caves were a source of building products for local buildings and habitats during times of conflict. In the 19th century, some quarries, including Ternaaien-Beneden, switched from underground to open-pit mining. In the process, they carved features like the Lost Valley.
