Ruhr Sieg Nord south of Finnentrop. Spawn point where the locomotives stop. 2D Trees End of the tracks. There is an invisible barrier part way up the hill.
I guess I am missing something - It is the end of the developed route... what are you looking for? Not trying to be difficult, but not sure what you want to see at the edge of the DLC.
Usually getting close to this causes the player to trigger a message and leave the game, but he has managed to circumvent this.