Maastricht
Caves in the Netherlands, and they are very special!

Caves in the Netherlands, and they are very special!

In the most flat country in the world there are caves, the caves of Maastricht in the Netherlands! They are not a natural phenomenon, but the gigantic system of corridors are completely excavated by humans. For the past 700 years the excavation resulted in a 220 kilometers long tunnel system! The marl that was mined there was used for buildings and