All my pics are on my iPhone 4 -- gone forever. But I've been to the cave and ruins twice, and many of the things I photographed are at this site, if you are interested. One of the coolest things from the American POV are the silhouettes of American soldiers who took refuge in the cave during WWII. The tour guide expressly spoke to me about these things, knowing I was on the tour: https://www.kasteelvalkenburg.nl/en/discover-our-locations/velvet-cave/