Like all linnorms, the cairn linnorm is terrifying: CR 18, a breath weapon of acidic bile and negative energy, a poisonous bite, and a particularly nasty death curse (Con damage and aging…per day). But perhaps the most terrifying thing about the cairn linnorm is hidden in its name. Other linnorms are creatures of the land, named after geologic features specific to the northlands. But cairns are manmade (or at least humanoid/intelligent creature-made). If cairn linnorms exist, it’s because we created them. By fighting battles, spilling blood, digging fortifications, raising mottes, and tearing up the earth or erecting cairns to bury our dead, humanity changed the world…and changed linnorms along with it.
This may explain why cairn linnorms have such odd diets and psychologies, hungering for corporeal undead while fastidiously respecting the sacred threshold inherent in every tomb. Perhaps some germ of a race memory remains in every cairn linnorm, reminding them of their genesis and insisting that the old borders between life and death are honored…
While the cairn linnorm Gloamfang slumbered beneath Goshawk Crag, fat on the carnage from the Oathbreaker War, the men of Lanark raised a massive dolmen around the beast. For good measure they then triggered an avalanche to bury it and erected standing stones at the four compass points, marking the rubble-strewn valley as a gravesite forever more—effectively trapping the dragon. There’s just one problem: The fourth standing stone is missing a glyph, because the man the standing stone was meant to honor was raised. Through that loophole the linnorm could crawl, if it ever got wind of it. When a scholar points this out in a lecture hall more than 200 leagues away, an eavesdropping quickling decides it is time to wake Gloamfang.
When the embalmed body of a saint disappears—along with the entire church and graveyard that went with it—leaving only a circle of mushrooms, the search naturally leads to the fey realms. As mortal religions and faeries don’t mix well, all such spaces that find their way into the Ælfwood are sealed away in one place, a pearl of a necropolis presided over by a cairn linnorm. The linnorm considers even then most newly arrived churches and gravesites to be his, and will not surrender the lost relic without a fight.
When the eccentric Bruno the Mad marched his crane-footed fortress through the Scarab Desert, watering drought-stricken oases as he went, the Priest-Kings of the Undying repaid his kindness by attempting to imprison him and steal the secrets of his famous conveyance. He responded by gating a particularly large cairn linnorm into the midst of the mummies’ most sacred city. The cairn linnorm has now devoured scores of lesser undead servitors, and the priest-kings themselves are essentially under house arrest…for while the cairn linnorm will not root them out of their sacred tombs, the heat-maddened beast prowls endlessly looking for a way at their rancid flesh. After months of this humiliation, the mummies are ready to reveal magicks never before seen by outsiders to the adventurers who can drive off the dragon.
—Pathfinder Bestiary 3 182