The Goblin nations are a loose cooperative of subterranean collectives around the continent. Goblin collectives are run like a business whose export is destruction. Their own currencies vary in exchange value against one another based on how destructive that clan has been in the previous quarter, and are mercifully not limited to committing crimes against humans. In fact they prefer to fight each other. As Fey, they are believed to share an affinity with Elves, although it has never been seen.
There is little that is certain about the scope or exact whereabouts of these collectives. Occasional sinkholes reveal the remains of their tunnel networks, some of which have led adventures to discover the remains of destroyed goblin cities. Even a razed goblin city should not be explored lightly. These dark places compound the dangers of spelunking, exorcism, and and the disarming of nonstandard ordnance. All this danger and more would be present should one set foot in a living goblin city.
Even when all the living inhabitants are dead, there are frequently functional remnants of their traps, devices, and machines. There can also be undead, goblinoid theri and haunts, demonic spirits, pits, alarms, and even gateways to Profundum. These dangers are quite the norm for goblins, and were chiefly designed with other goblins in mind.
Despite their pernicious destructiveness, goblins are far from unintelligent. Goblins actually exceed every human society in terms of literacy and maths.
Their academic achievements are attributed to the goblin rite of passage called the brand of doom, in which every youth is branded with the rune of their own small, nameless demon companion. The rune creates a psychic mind meld between each goblin and their own demon spirit that can guide them and teach them, help refine their ideas, keep them company, and generally help out... while also learning every single thing about them to an unsavory degree. Thus there are no goblin schools, yet they're all darkly brilliant and consumed by destructive tendencies. Most humans never learn this about the rune; all they know is that should a goblin bearing the rune ever fall in combat, it catches fire and explodes, often setting additional fires. Since goblins above ground are quite rare and their tendencies are so well known, no further explanation is ever sought.