Sint-Pietersberg Caves

The hill south of Maastricht is soft yellow limestone, and people have cut blocks out of it for centuries, leaving a network of tunnels that runs for many kilometres under the plateau. They are called caves but nothing about them is natural: square-cut corridors, saw marks on the walls, and layer upon layer of charcoal drawings, names and dates left by quarrymen and visitors. You can only go in with a guide, and inside the temperature sits around ten degrees whatever the weather is doing outside. The rock itself is full of fossils, and the first mosasaur remains ever described by science came out of this hill. Above ground the abandoned cement quarry has been handed back to nature, with chalk grassland and orchids on the slopes.

What you actually see

• The quarried corridors - straight square-cut passages with visible saw marks, running far under the plateau.
• Charcoal drawings and inscriptions - centuries of names, dates and sketches left on the soft walls.
• Fossils in the rock - shells and sea creatures embedded in limestone laid down when this was seabed.
• The old quarry above - the disused cement pit, now cliff faces, pools and chalk grassland with orchids.

When to go

Tours run year-round and the underground temperature never changes, which makes this a reliable option in bad weather and a cool one in a heatwave. English-language tours are less frequent than Dutch ones, so check times and book ahead, especially in school holidays. The grassland above the caves is at its best from May to July.

Honest expectations

You cannot wander: everything is a timed group tour on a fixed route, and the guide's language may not be yours. It is cold, damp and dark, floors are uneven, some passages are low and narrow, and there is no phone signal underground. Bring a jacket even in August. Anyone uneasy in enclosed spaces should skip it entirely.

Nearby

Maastricht is a twenty-minute walk north, with the Jeker valley and the Belgian border close by.