The information we receive through the images gain another meaning if we take the account the invisible. Not only their existence, but also the relation with the visible.
As the plumber who gets a guide wire in order to find which way it does inside the wall. In fact, the journey inside a tunnel does not reveal how the mountain is outside. For those inside the tunnel, only matters to find a way out. Physically, it can be a uncomfortable experience if the tunnel is too long, or if the path has no way out.