Except for their glowing eyes, cairns seem no different from living stone giants, largely because their flesh resembles stone. Thus, when the creature's eyes are closed or otherwise not visible to an observer, it can be virtually impossible to tell the difference between a living stone giant and an undead one. Given their appearance and stiff movements, cairns could be mistaken for large stone golems. Cairns are not mindless undead but beings with as much intelligence as they had in life.

Combat: Cairns have a keen telepathic sense that enables them to tell when someone comes near even when that person is silent and/or invisible. They make good use of this when waiting for victims in ambush positions, closing their bright, betraying eyes and blending in with the rocky background until the intruders come close enough to attack. Because of the giant's stony appearance, victims have a -5 penalty to their surprise rolls when they encounter a cairn underground. Often the first hint of trouble is when large boulders start whizzing past them, hurled with incredible force (3d12 hp damage instead of 3d10 for live stone giants) to a range of 350 yards. Cairns inflict more damage with physical blows and weapons than they did in life, causing 1d10+8 or 2d8+8 hp damage respectively. Their undead nature penalizes them with a loss of Dexterity, however, and cairns cannot catch hurled stones and other large missiles as they did in life.

Cairns are slow but formidable opponents. Aside from their excellent armor class, they are immune to all weapons that are not of +2 or better enchantment. They are also immune to mind-affecting magic, sleep, hold, petrification, poison, paralyzation, and cold- and earth-based attacks. Holy water harms them; each vial inflicts 2-8 hp damage. The stone to flesh spell reduces their armor class to 0 (as it was in life) for a full turn (10 combat rounds), while transmute rock to mud actually reduces it to 7 for the same period of time. Note that weapons of +2 or better enchantment are still needed to damage the creature. Raise dead slays a cairn instantly, and although sunlight does not harm these creatures, they abhor and actively avoid it.

Habitat/Society: Cairns dwell in mountain caverns, just as they did in life. They never dwell in groups of more than three, however, and even these small gatherings are rare. Undeath brings with it a sense of isolation and desire for solitude. Some cairns deliberately distance themselves from their former clans to eliminate the possibility that they will return and destroy their old families in a jealous rage at the fact that they are still alive.

Ecology: Cairns have no effect on the local ecology, for they eat nothing, being sustained wholly by energy from the Negative Material Plane. Animals sense the presence of these giant undead and stay away, but these creatures generally choose the bleakest and most lifeless regions in which to dwell anyway. Although any vegetation within a quarter-mile of a cairn's lair withers in a matter of months, they lair in areas with little or no vegetation, to begin with. Their body parts are favored by mages who seek to make magical items connected with petrification or stone-based spells, and research is being conducted into the mysterious inner sense that lets them know when intruders are approaching, as such a power might be used in the construction of ESP-related items or potions.