Casemates 

The famous Casemates tunnels are located underground and were dug to defend Maastricht against invading forces. These tunnels were used by soldiers during sieges of the city to 'surprise' the enemy with an attack launched from underground.

In the lovely Waldeck Park, you can already see a number of above-ground defences during a city walk. But there is more... An underground system of tunnels that is so extensive that it makes this Kazematten network unique in the Netherlands. Perhaps more interesting is that the Kazematten tunnels of Maastricht were not only used as an underground shelter but are actually the only location in the Netherlands where an underground war was waged. This is not possible anywhere else in the Netherlands because of the groundwater levels. Both of these uses have left the expected, yet poignant traces which remain visible to this day.