The series starts with Advanced Adventures #1: The Pod-Caverns of the Sinister Shroom (for levels 2-4). It was one of the first published products of what is now called the OSR, coming out in August of 2006. Matt Finch (of Frog God fame) was the author and in the module was an underground river called the Shadowvein. The Shadowvein wasn’t detailed, but in the module Matt put forth the idea that PCs could approach the Pod-Caverns from the river and go up to the surface, as opposed to going down. That idea stuck with me, but the chances of a low-level party spending any serious time underground seemed slim to me, given that the history of the game has the underdeeps a nasty high-level place.
After publishing another 20 or so Advanced Adventures, I finally decided to make the underdeeps (at least the not-so-deep-underdeeps) a little friendlier to low-level play and wrote the following two modules #23 Down the Shadowvein, and #24 The Mouth of the Shadowvein. These two adventures (levels 3-5) allowed lower-level PCs a chance to experience the depths without getting immediately TPKed if they were good players.
I’m attaching the GM’s map to this post. Hopefully you can feel the same feeling I do when I see it – a sense of wonder of what yet is to be discovered. Honestly, I’ve considered a Kickstarter campaign to flesh out more of the unexplored hexes, but haven’t decided on such. I think it would be cool, but who knows how many others would? Regardless, this map shows what The Shadowvein Series tries to, and hopefully succeeds in, doing.