Marl quarry

Michel Brouwers has added a photo to the pool:

This quarry is located near the village of Bemelen, 2 KM east of Maastricht. The quarry was dug out in a hill, the so-called Bemelerberg. The hill itself is actually part of a plateau that ends at the Maas bassin. Marl can be found in the entire area, though not always as easily reachable as in Bemelen.

For more on Bemelen (only in Dutch): nl.wikipedia.org/wiki/Bemelen.