Giants are big. Caves are not. Usually. It depends on the cave. But the confines of the Lands Below are cramped more often than not, so it stands to reason that a species of subterranean cave giants would be among the most stunted and degenerate of the lot.
(Degeneration also explains their affinity for axes despite their inability to smith them—perhaps they had the craft knowledge at one point, then lost it over time as their society waned. The Golarion setting’s Earthfall is the type of cataclysm that could have sparked such a decline; for 3.5 fans, similar events occurred on Oerth, Krynn, and Mystara.)
Then again, brutal humanoid societies have their own Darwinian logic. Maybe cave giants aren’t degenerate giants, but really big ogres and orcs.
Cave giant encounters are a great way to throw a bunch of monsters at PCs, possibly all at once. A typical tribe, for instance, features cave giants, two giant lizard species, and dwarf, orc, and troglodyte slaves. That right there is a readymade night of combat—just draw a map and you have an adventure. And one out-of-place NPC found in a cave giant slave pen—from a hissing snake-man to a purple-skinned elf to a tiefling with a demon-grafted limb to a barbarian from another age—could point the way to any number of encounters deeper in the earth.
The great secret of the Steelgrip tribe is that they partner with cave giants to forge their famous axes. Cave giants work the bellows, push carts of ore, and test out new design prototypes on other humanoids—including dwarven prisoners. Other dwarves would regard this as treason, and the Steelgrips will kill to protect the secret.
A famous smith has been abducted by cave giants and put to work crafting axes. If the party does not rescue him in time, he may lose a foot (but never a hand) to one of his captors’ hungry lizards. If they do rescue him, foot or no, he won’t want to return immediately. During his captivity he found a seam of skymetal, and he will risk gangrene to follow it to the source.
“Lizards? I crush lizards.” So says Serg, chieftain of the Land Dragon tribe. The “land dragon” in question is actual an immense tortoise. The unstoppable tread of this Colossal beast has allowed the Land Dragons to move out of the caves and into the badlands. Serg can’t really control the tortoise, but for now he is content to let the beast do the navigating. As it follows the spring flowering of dawnglory cactus plants, the cave giants raid any towns or caravans they come across along they way.
—Pathfinder Bestiary 3 127
Lots of comments on the caulborn, including role-playing input from demiurge1138, a stat conversion from filbypott, and Todd Stewart and Kinak are both pushing me to read James L. Sutter’s Redemption Engine. (Embarrassing confession: I have not read a single Pathfinder novel yet, though Know Direction’s Ryan Costello Jr. has given me a reading list for when I finally get my feet wet.)