Sliding ambient light down doesn't make darkness

Hi, I have a area inside a pyramid that needs to pitch black, but even though I’ve turned the ambient light level to black and also did the same for fog, the inside of the (sealed) pyramid still has plenty of ambient light. What do I need to do to get the light levels inside the pyramid down further?

Note: The pyramid uses a Diffuse shader.

Thanks.

First thing is to make sure under the mesh renderer of the pyramid both cast shadows and receive shadows are ticked. Then it depends on what type of light you are using.

Also check the shadow type and strength from the light sources you are using