Yeah this has been bugging me for a while actually. Old rail lines, old mine shafts, old drainage tunnels - theres a pattern there that nobody really talks about. My working theory is its less about the physical structure and more about what these corridors represent energetically, basically long linear disruptions through the landscape that might function as conduits for something crossing over.
Cornwall has loads of old industrial infrastructure and I've had two experiences near abandoned mine workings that I'd rather not go into detail about publicly but lets just say the "dog" description makes more sense to me now than it used to.
Anyone mapped the sightings against railway OS grid references? Would be genuinely interesting to see if there's clustering at specific points like junctions or tunnels rather than just anywhere along the line. Junctions especially would fit with the interdimensional corridor idea quite neatly.