Black Dog Run Valley is an area of Shropshire not normally accessible to players.
This valley is situated in the middle of Shropshire, and is not actually used for any part of the story. Normally players would not even be able to access this area, though you can get a peek at it by way of the areas around it. For example, there is a gated entrance to the valley along a secluded path in the area of the Lakeside Holiday Camp.
Entry gate to the valley at Lakeside