The Michelin Guide's review
This hill lying between the Meuse Valley and the Geer Valley is known for its caves, the product of quarrying excavations since Roman times; the extracted marl stone was used for building works in Maastricht. Today, a network of galleries running for 200km survives, 12m high in places and decorated with charcoal drawings. The sedimentary rock offers up many fossils. Traces of habitation in the caves.