One thing I have not been able to re-locate in my internet searches, is the website which talked specifically about the symbols and writings used by the stone masons, mostly medieval in time frame. What I read at the time (several years ago), was that the masons used these symbols to navigate, describe the various qualities of the stone, mark the stone for future cutting purposes, mark their own unique identifiers (in other words they perhaps had symbols which identified them as individuals), and in some cases it appears that there were marks made which had to do with societies which were formed as a result of particular political or other purposes, and for which people at the time could have gotten into some real trouble had they been deciphered. I found it all rather interesting. I have not been able to locate any of this.
The other item I have not been able to locate, was on the particular shaping of some of the mine walls, which kept them from caving in. One mine I read about sloped the walls to the ceiling in a more pyramidal shape, and thus was able to excavate much larger passages that normal recatagonal/square cuts. All very interesting.
The pictures I also recall were of very high quality. I have been rather disappointed in the quality - lighting, grain, for example, of some of the pics I have viewed. A good high quality flash and/or light source taken with a newer digital camera does wonders. I wish I lived in the area, as I would sincerely like to do some exploring and take some high quality photos.
Best,
David