An extensive series of man-made caves formed by the quarrying of stone used to build the city. You can take guided tours around two different parts of the caves, starting either at Chalet Bergrust or Buitengoed Slavante. The caves' temperature is a stable 9-10 degrees, so a trip can provide relief from a hot summer's day. The complex has often been used to provide shelter during wartime and in places you can see old stone stoves used for cooking by people hiding in there. The cave system is very extensive and stretches a long way across the border into Belgium. In the caves on the Belgian side, famous brewer Pierre Celis (inventor of Hoegaarden Wit) matures his Grottenbier, taking advantage of the stable temperature to bring out the flavours perfectly.
Details at the city's tourist information website at www.vvvmaastricht.nl/Dagjeuit/moreinfo.php3?ID=55&lang=en The entrances are a couple of kilometres south of the city centre on the west bank of the River Maas.