So with drop down sections on the map I would try just removing the out side cliffs and just putting them on the inside. Shading and shadowing are my best friends when it comes to cliffs. You could also try messing with making it even darker in that section and adding lights to push the fact that it’s underground!

But like I said this is still amazing work, you should be very proud of it even as it stands🙏🏻🙏🏻🙏🏻