[Idea] Underground Grotto Type World

I don't know if anyone will know the reference, but in the series Troll Hunters—Troll Market—is amazing. I would love a sunless/seasonless/weatherless underground world for occults, and fantasy players. The Forgotten Grotto is a great starting point to how the world could look like.

It would be great for vampires to be able to live without fear of the sun, werewolves without the effects of the moon, and basically a place where all occults (maybe not aliens) can congregate. Season specific plants can grow year round as they are auto "sheltered". And if you add Troll (or Goblin) occult OMG, that be amazing with a human disguise form.