A major Belgian tourist attraction (around 250-300,000 visitors per year), the caves are located in Wallonia, on the outskirts of the village of Han-sur-Lesse.
The caves were formed as the result of an underground erosion of a limestone hill by the river Lesse.
[1] Access is only possible via a vintage streetcar, a remnant of the country's once extensive vicinal tramway system, which departs from the center of Han-sur-Lesse.
The guided tour takes about an hour to an hour and a half and includes a sound and light show in one of the largest chambers of the cave system and an ending with a simulated cannon shot to demonstrate the caves' acoustic properties.
Visitors used to exit the caves by way of a short boat ride at the point where the Lesse emerges on the surface, but since 2009 this has been replaced by a bridge.