Far beneath the surface and mountains of Avanor lie the great and expansive Underhalls; home to vast tunnels, halls and grand dwarven cities carved out from the deepest stones. The Underhalls were created by dwarven refugees shortly after the fall of the Don Bazradi city of Kongsbarad. They escaped under the mountains away from the onslaught of the Pacts and established a new, vast kingdom deep underground. It was at the end of the Time of Suns, before the Old Imperium had been founded, that the tunnels began to go deeper underground, and more cities were built to further support the rapidly recovering dwarven population.
Much of the Underhalls were originally created by the Kha'gazur dwarves, and had been abandoned for thousands of years since the Time of Stones and Iron. The Durgheil Stone Clans claimed the Kha'gazur tunnels and citadels after Don Bazrad's fall, and in time they expanded these tunnels even farther. The Underhalls go as far as from the very northeastern mountains of Avanor to the continent's southwestern reaches. Some parts of the Underhalls go far beneath the deep seas, and touch lightly into the domain of southeastern Norrhan.
The Underhalls, in simpler terms, are divided into three layers; the Upper Levels, the Lower Levels, and the Deep Levels. Anything within the Upper Levels are mostly safe, as dwarven patrols maintain the tunnels and guard them from any dangers that might creep from the depths. Most of the grand architecture has avoided deterioration within the Upper Levels, and the majority of standing dwarven cities are found here.
The Lower Levels pass into the parts of the Underhalls where lava and gasses begin to endanger and pollute the air. Most of the tunnels, halls and cities within the Lower Levels have been abandoned, though some cities have managed to adapt themselves; surviving the harsh depths by mining the more valuable minerals there, and trading with surface-dwellers. Many parts of the Lower Levels remain unmapped, and it is a place of many battles between desperate dwarves.
The Deep Levels are where the Darkborn numbers are greatest. Few maps detail anything about these levels, and any expeditions into the Deep Levels rarely return. The air is so thin that many begin to hallucinate and go mad; though many believe that it is not always the air that gets you. Whispers from the darkest depths corrupt the minds of anyone traveling the deepest tunnels, and no one can truly say what the whispers are or where they come from. Only fools would venture into the Deep Levels, yet there are many fools willing to find the riches of the ancient, abandoned dwarven cities.
The Underhalls were meant to be the second chance and rebirth of the Durgheil people in Avanor, yet their kind did not take too long before they started to turn on each other for conquest, resources and the very valuable minerals of the deeper tunnels. Ambitions saw the rise of many dwarven kings, most of whom could not unite the dwarven people under one, single kingdom; leaving Thane Councils to rule over the many independent underground cities.
When the Black Blood Curse spread from the city of Orthavir, many of the Underhalls' tunnels, halls and cities were abandoned by their inhabitants or conquered by the Darkborn. The increasingly rising strength of the Darkborn dwarves, who were created by the Black Blood Curse, saw the fall of many dwarven cities, until only a few remained. Most of these cities were on the upper levels of the Underhalls, and a few of them still stand to this day; having established strong defenses against the dangers that now lurk within the deepest reaches of the dwarven tunnel networks.
The dwarves who live in the Underhalls are dominantly of the Stone Clans, though there are a few Iron Clan descendants from the days when the Barador Empire fell and crumbled into the kingdom it is today. The dwarves' lives are rough and hard, as surviving underground is made dangerous by threats ranging from tunnel cave-ins to Darkborn raids to the violent bickering of their fellow brethren. The cities hold on merely by fragile, thin alliances, and often enough there are ambitious would-be-kings who wish to unite the cities for their own purposes; often on the promise of retaking the deeper levels of the Underhalls from the Darkborn. However, none know where Orthavir's (where it is believed that the Darkborn home is) location is at, since most maps of the Underhalls only cover a fraction of the vast network. Rumours say that Orthavir found its way into the Underneaths; where beings of unimaginable terrors reside.
Aside from the Darkborn or other dwarves the Underhalls are home to many other dangers and creatures; many of which have yet to be discovered. The Aedh Shavai elves, after their exile from Daln Ashelaan, traveled into the Underhalls and established their new home within the abandoned cities of the Durgheil dwarves. While many of their kind were forced to the surface again by the Darkborn, some of their cities still remain not only within the Underhalls, but deep within the realm of the Underneaths.
Some orcish clans and goblin tribes also reside within the Underneaths. Their kind are far less peaceful than their surface brethren, as the challenge of surviving underground has made them creatures of desperation and violence. The Underhalls is a place where only the strong survive; leaving little room for trust and peaceful ventures. Even so, many surface-dwellers travel into the Underhalls in the hopes of finding anything from rich veins of ore to recovering lost dwarven secrets or treasures.