So I recently took greater notice that many of my favorite gaming writers will post little snippets of what they've been working on to their blog. Even if it's incomplete, it's still a solid preview, can build hype, and is probably somewhat usable on its own. So why don't I try that?
My home campaign setting is called Underworld, and is all about that sweet, dank Underdark, baby. When I first started working on it, I spent a long time thinking about how to bring more out of the Underdark experience in D&D. How much depth would need to be added in order for that one trope to carry an entire campaign? And I like thinking in terms of rules and mechanics at least as much as lore, when it comes to worldbuilding and reinforcing themes.
The following materials were mostly written around 2016 and 2017 but I was heavily sidetracked by worldbuilding and "higher level" game design. Oh, and getting a bachelor's degree. But I consider all of this to be stuff that I one day will return to and do justice, because it's important (in fact, I made a couple edits as I copy/pasted it here). I anticipate eventually either putting this stuff into a Brave supplement that'll have rules, systems, and tables for Underworld stuff, or I might just compile and publish my setting outright and put this stuff there instead. Contained within the following thoughts are some implied setting assumptions that may not be true for the "default, vanilla" Underdark, but you'll still enjoy it. Plus, I included lots of great pictures you'll want to expand.
And yes, the release of Veins of the Earth did stifle me a bit. But while that book is indeed excellent, I also think you'll agree that much of what follows builds onto it quite nicely and covers things it doesn't address.