This particular poem has played with my imagination ever since I was a kid. As a child I imagined the traveller was human and alive, just like all of us. I imagined that while travelling, he found himself in front of a haunted castle.
Recently I read it again... and instead of looking at a weary 'human' traveller wandering off into ghostly realm. I began to see a ghostly traveller lost in darkness, in his search of the light. The darkness symbolized by the night. This ghostly traveller is tired and weary and by mistake he stumbles upon our realm. The worldly realm. People from our realm cant see him, can't hear him. And he can't see us. But we both sense each other's presence.
And then I read 'Some One' another poem by Walter de la Mare and I couldnt help but see a connection.
But then again, for all you know I'm just overworked and my mind is running ahead of me: -)