How to make dark area?

Hello! I have a map with dirrectional light etc and my map has a tunnel which goes underground. How do i make it so the underground has a darker ambient light than the rest of the scene?
Map is built in runtime from props.

Hello there.

You can ake a “trick”.

If you have directional light, you can create a gameobject over the area so it makes a shadow. But you do not want this obejct to be rendered.
If you look at that obejct inspector Renderer component. You will see can select different types of shadow, and also can select a option “Only cast shadow”, so the object itself will be not rendered, only the shadow will.

Also know that if you apply to the object a transparent material, Alpha value will change the strenght of the shadow.