I've added more to my new work. here it is as of right now.
To see the step by step process read on after the break.
I added a worn path to the cave so it looked like it was being used.
Here a curves adjustment layer clipped to the path to give it some contrast and depth.
I added a door knocker that looked like a skull and then blended the color in with the door.
A curves adjustment layer for the doorway to darken it some more.
I added another blank layer with a multiply blend mode and
painted in more shadows around the door with a 3% fill brush
I continued darkening the doorway and adding different colors to help it blend in better.
I squared of the top of the door shape and sharpened the edges.
I nitpicked the path next to the door a little so it looked like it went inside.
Finally I added a couple Red Tailed Hawks flying in the distance for a little more visual interest.
I'm still not completely sold on the door and may make more changes there.