I entered a contest for SOTA (Shroud of the Avatar) to develop a full environmental scene. I decided to create a completely underground abandoned cityscape, fantasy genre. I used CC3 to generate a map for the layout first, which you will see correlates with the environment if you play the web version of the game: http://massivespace.com/sota/web_player.html
I used several asset store plugins including the music, some sound effects, the modular caves system, and 3D Models. My only goal was to put everything together into a seamless scene. There are lots of secret places hard to find, but the caverns are very large. I utilized a lot of environmental audio as well. Check out the temple ruins and the Waterfall of the Gatherers.