In the south of the Netherlands, near Maastricht, lies the plateau of Caestert, which consists largely of limestone. The northern part of the plateau forms the Sint-Pietersberg. In the Middle Ages, people discovered that limestone was a very useful building material and started excavating it by hand, sawing out the soft stone one block at a time. Over the centuries, this industry led to an immense underground labyrinth, referred to as mergelgroeven (marl quarries).

The surface of its walls contain a huge archive of information, notes, drawings and inscriptions dating back to the late Middle Ages. Left behind by a variety of people, from blockbreakers to tourists, from soldiers to researchers and from priests to everyday passers-by. This history book in stone gives us insight into life underground as well as on “ground level”. It is where the infamous Mosasaurus was first discovered. It has witnessed wars, sieges and liberations. It is home to many myths and legends and was used as storage for national treasures such as Rembrandt’s Night Watch.

Around 1960, a cement company began excavating Slavante, the oldest part of the tunnel system, heralding the start of the destruction of this cultural-historical treasure. This prompted several people to start documenting as much of the system as possible, before it disappeared into the cement mixers forever. One of them was Jan Spee, who took thousands of photos in this underground maze. He meticulously mapped and organised its body, adding notes, descriptions and thoughts to them. At the end of 2013, he transferred his entire collection to the archives of the Historisch Centrum Limburg (HCL). His photos alone take up 5 linear metres of shelf space, the total collection spanning over 21 metres.