What this is all about:
After I finished H.P. Lovecraft´s story “At the Mountains of Madness” the GM in me dreamed about an adventure that would be take place in some (other) subterranean ruins of the Elder Beings. Another city or outpost, perhaps smaller, or just the caverns that would lead to its entrance. An adventure about the strange creatures that could have developed there, based on some breeding stock the Elder Beings once kept. I thought about the Elder Beings attempting to slowly retake those places they left as they moved back into the oceans so long ago. I thought about a renewal of their conflict with the Mi-Go, one that is only at the beginning as Mi-Go recon parties try to locate and gauge the erstwhile settlements and strongholds of their rivals. And about what could happen when a party of (demi-)human adventurers would stumble upon all of this, on their search for riches or ancient wisdom.
As I was not able to create a full-blown adventure out of my ideas, I rather created a set of 20 structured encounters. The difference to (completely) random encounters is that some of them are preliminary encounters that will trigger certain other encounters as a follow-up (or will be triggered instead of their follow-ups). In addition, a simple frame was given for the encounters and stats for six creatures and two strange items [all of whom are compatible with Lamentations of the Flame Princess(tm)].