The Pitjesberg is a special underground marl quarry partly located under the old village centre of Zichen, municipality of Riemst. This tunnel system is a series of different excavations and 'pits'. Over the past centuries, dozens of underground marl quarries have been created in this village, many residents extracted marl by means of a so-called shaft extraction under their property. The tunnel system was almost always made accessible by making a 'graet', a diagonal tunnel or staircase from quarry to ground level or cellar. The often small tunnel systems that were created in this way are called 'pits', later they often became connected. By means of excavation direction research it can be determined from where a tunnel was extracted. In this way it has been discovered that slightly more than half of this tunnel system consists of a series of pits. This area is concentrated under the houses and along the Kerkstraat. The part under the meadows and gardens, up to the Kerkstraat, was extracted from two valley entrances. Here an underground extraction has been started on a slope where the marl once came to the surface, which has resulted in a large system of tunnels.