I started systematically going back through my old files trying organize and see if I missed any silhouettes opportunities. I found these pictures from an old book on rock climbing in Great Britain that I never did anything with. I thought they might be useful if you are doing a point crawl and want to give layers a visual sense of a lair or just a local landmark. Like these map insets.
Update: Found another one somewhere else. I guess I like pictures of rocks. Also, a picture of Fingal's Cave which is more a dungeon entrance than landmark, but could be both:
These are all public domain, use them as you wish.