De Keel Quarry is very unusual as it is situated across an international boundary; the boundary however arrived far after its undeground voids had been excavated. As the majority of the quarry lies beneath modern day Netherlands, it is listed under that country.
The current entrance to the quarry is off the Albert Canal cutting, the former entrance passageway having being destroyed during the canal’s construction. The name comes from the nearby settlement of Keelveld. It is believed to have started as three separate excavations, which were gradually linked over time.
Mining took place on several levels and individual passages are up to an impressive 8 metres in height. Around 7 kilometres of tunnels were cut. Mining continued until the 1960s, although in latter years most of the output went for cement rather than building stone. Parts of the quarry were later used for mushroom farming.
The quarry is now gated and is an important bat habitat.