can't wait to see the result!! i give you an idea, if you like it thats some crazy advanced stuff involving daynight animations: i tried something in my latte inouterior tileset, basically i had windowed skyboxes and light sources controlled by day/night animations (that need to be set on in toolset cuz default for interiors is off, if there is no edit of tilesets 2da stuff), so when you look out of the window, the sky changes from day to dusk to night to dawn and so on, same with lamps... they light at dusk and light out at dawn.
with your master skills you should be able to do something like that, maybe for cave entrance tiles and groups.
there is a lockwood painting i always found amazing and so inspiring, it really fits teh idea im trying to describe:
www.artistsuk.co.uk/acatalog/Sojourn_Todd_Lockwood.jpg