And here is the photo I took just because it looked so out of place in the landscape. It wasn't until I got home and started researching that I found it was remnants from mica mining back in the Roman days. They say as you climb you will see the remains of some old Roman mines where they used to mine for Mica, as you climb you can actually see the seams of Mica. Well I didn't know so I didn't really notice. It would be fun to investigate.

Interestingly, Castrojeriz started out as a place for the Roman soldiers to guard the Galician gold mines.