Between 1575 and 1825, a network of underground passageways or casemates was created on the western side of Maastricht. During times of siege, these tunnels were used to shelter troops and supplies; attacks and counter-attavcks could also be made from their safety7.
The whole network extended to 14 kilometres and was extensively used in World War II as public air-raid shelters. Although much of the above ground defences have disappeared, beneath ground tunnels with fine brickwork still connect magazines, firing positions and listening galleries.
Today, guided tours can be taken of this fascinating site.