Showing Depth in a Hole

Holes are funny things - if the light doesn't shine into them they just look like a black round disc. Especially on a 2 dimensional photograph.
You actually need to shine the light in at an angle so it lights one side of the hole and then reflects to the other side - but not as brightly. This will create the feeling of shape.

You can have the reverse situation happening when you are in a dark building or cave and there is a deep hole in the ceiling. The light has to strike the edges and reflect down to light up the surrounding materials

The photos illustrate the different light and its effect. The top left are lava tubes, but the holes look like black blobs because the light is diffuse - non directional. The bottom left shows a tube with light shining down it, showing depth and texture. The one on the right is the reverse, the light bounces around an reflects down into the room.