From publisher blurb:
When civilized races first began constructing their dungeons, one of the first discovered creatures were the delvers. This intelligent race lives deep underground, burrowing through caves and bedrock to design elaborate lairs. While not especially antagonistic, many delvers came into conflict with surface races who encroached into their territory.
Most delvers dug deeper to maintain their solitude, but a few proved willing to engage with dwarves and surface races in trade. In exchange for food or protection, delvers agreed to help craft their dungeons. While initially skeptical, most races ultimately accepted these deals when they realized delvers could forge tunnels far quicker than their own craftsmen. A few even convinced delvers to breach the dungeons of rivals, allowing armies to quickly reach their enemies.
Despite their monstrous appearance, delvers are not mindless beasts and will respond in anger to anyone attempting to deceive them. At a minimum, surface dwellers who attempt to betray the delver’s favor can expect their expensive armor to be destroyed by acid, leaving them naked and defenseless underground.