Generic Fantasy World 182
This world is full of magic and wonder. There's many towns in this world, but where they are situated does not matter.
All elements of 5th edition can be found anywhere in this world! There isn't an "underdark" per say, but there might be an underground land, and the creatures associated with such a place probably exist there. What is clear is that a lot of overlap in inner planes exists within the material plane, so all sorts of wacky stuff can happen.