Grotten Noord, like the Zonneberg cave, is not a natural cave. It is actually a quarry that was started in Roman times to mine the marl that makes up St. Pietersberg (St. Peter Mountain). While a smaller group of chambers, Grotten Noord’s history began with Roman miners and includes several instances of Maastricht residents hiding from invaders, and even evidence of an (unsuccessful) attempt by Napoleon to blow up St. Pieter Fort.
Fun fact: the red church tower over the Vrifholf square use to be painted red with ox blood to prevent the marl from turning black.
Grotten Noord is an easy 20 minute walk from the Maastricht VVV. They offer English language tours on Saturday and Sunday from April 11th to June 28th at 2 pm. The tour costs 4.90 euros. The Maastricht Underground website is cute (it’s in Flash) but in Dutch so if you have questions I recommend you ask at the VVV. The website indicated that the cave was handicapped accessible, but I would disagree with that assessment as the path down is fairly rough and the path inside had some short steep parts.
If you are around when Grotten Noord isn’t offering English tours, try Zonneberg from July 5th to September 6th daily at 1:50 pm. It is further out of town (ask at the VVV about the bus), but larger and has more World War II history associated with it. I’d recommend both tours to pretty much anyone who can sustain a steady walk and isn’t afraid of the dark.
UPDATE: I forgot to include the link to my Flickr photos. Check em out.