The fantasy underground, the underworld, the caves, the depths ... that's a whole new world below the surface ...
... or, at least, it should be the new, exciting world below surface. I'm mentioning that because oftentimes, the world of underground gets reduced into just a few loot-filled dungeons to rob, a bunch of tombs crawling with things to kill, a couple of claustrophobic places to freak out in, a monotonous mist of darkness to feel insignificant in ...
The question follows: how should an author turn the underground into an engaging set of environments of their own? You know - unique places with their own dynamics, flow, life, and style.
The psychological aspect of dark, unknown environments is a rather cheap one; still, if needed, it can be emulated by almost any unlit, enclosed place (no need to reduce the vast spaces of underground into that). On the contrary, it is time to turn on the lights in the underground, to illuminate the spaces and let the spaces breathe ....
Underground cultures, ecosystems, cities, creatures, possibilities ... are they waiting to be discovered? Can the nothings of underground places be transformed into more humanized, appealing, and if not special, then at least distinctive forms?
How would you approach this?