The whole Area is of the finest sandstone and has been a querry already in ancient times.
Even when the Germans conquered the lands they where knocked off their shoes by what they found, they censored it:
Here another photo of these ancient big quarry shafts
Here one getty Picture in that houses have been built in the "quarry"
http://www.gettyimages.de/detail/nac...re-id501377745
unfortunatly it is still used as a quarry and knowbody knows how many ancient Caves have been destoyed already.
Here you can see were they hit some caves: