In settings where there are long established underworld thief, criminal and otherwise ne'er do wells there is going to be a system of heraldry associated with those who live in and rule from the shadows.
There are gangs, there are biker gangs, there are terrorist organizations, and then there are the Sons of Scorpions
A little way up the narrow valley, before they reach the woods, the PCs notice the squat, tumbledown buildings by the riverside. They are hardly big enough for a human to stand in, and the complex cogs and shafts that occupy the central cavity of one of the buildings are perplexing. What were these buildings? And how safe are they to explore?
Alternatively a desolate place is the perfect setting for a derelict chapel or croft. There needn't be any actual physical encounter involved, but it adds atmosphere to a place to see its dead history. For instance, in the Outer Hebrides there are whole deserted villages which were razed to the ground by the English during the Clearances. Such stories give a setting authenticity and character.