I relit the Environment Set by NatureManufacture as a foggy night scene. I wanted to light a natural environment that had both foliage and organic shapes (like rocks and terrain), and to learn different types of fog. To give variety in the layering of the fog I used Volumetric Height Fog, Fog Sheets, and Volumetric Fog Particles. For the Sky Sphere and the Skylight I used Unreal's HDRI Backdrop feature using a night HDRI from HDRI Haven.
Environment Set:
https://www.unrealengine.com/marketplace/en-US/product/environment-set