An open room lay before them, occupied only by a few cobwebs and dust. Upon entering, a phrase is seen on one wall. One of them utters the phrase out of wonder for its meaning, unknowingly activating the room. An eye opens on the wall in front of the poor souls and with a quick flash of light, the last thing heard from the room is heart retching screams... then silence.
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.