My problem can be seen here notice how the shadows don't change intensity or color when moving indoors to the cave. The only thing that changes is the highlights when I move under the directional light. I was thinking about adding global illumination but I don't think that would work with a toon shader. How can I get my lighting to become darker once I enter indoors e.g a cave. Thanks!
One solution is to setup light probes so your dynamic objects receive bounced light information from the static environment.
As explained in the manual: Light Probes for moving objects.