Caves of Folx-les-Caves

The caves of Folx-les-Caves in Folx-les-Caves, a district of Orp-Jauche in Walloon Brabant, are not naturally occurring caves but galleries that were hewn out centuries ago as underground quarries.
They are located at an average depth of 16 meters and cover approximately 6 hectares. They consist of a two-way system called the 'Caves Bodart' and the 'Caves Racourt', which are connected by one closed passage. An underground stream that flows into the Kleine Gete runs through the caves. The caves are hewn in an arch shape. They have a height ranging from 2 to 4 meters with peaks reaching up to 8 meters. The remaining supporting pillars are spaced 2 to 8 meters apart. The walls show numerous chisel marks from when they were hewn.
There are no written sources or studies providing clarity on the origin and age of the caves. The caves already existed before 1606. A book from that year by Jean-Baptiste Gramaye describes the “caverna subterranea.” The oldest inscription in the caves bears the date 1771.

Wikipedia