The Deep Earth; also known as the Deepshaes, is the portion of the Underdark that exists beneath the Moonshae island chain. Like its surface landmass, these caverns have been largely isolated from the rest of mainland Faerun (and its Underdark) for a long period of time. They were formed over the millennia by water eroding the porous limestone rock in places and carving out huge caverns in the Underdark.
In a rough approximation to the islands above, the caverns of the Deepshaes lie below their surface counterparts but are linked via a variety of means (rifts, dwarven tunnels, connecting caverns, shafts, etc) although over time some of these Underdark highways have ceased to exist and one or more of the caverns are isolated from each other.
Fresh and salt water is in abundance in the Deepshaes (in stark contrast to other regions of the Underdark beneath mainland Faerun), which has led to a vibrant selection of life in the lands below, with fungal forests and even a unique species of Underdark tree found nowhere else in Faerun.
The Deepshaes are abundant in all forms of ore and gems, and is even home to an unusual substance known as “Living Metal”, furthermore, the dwarves of ancient Ahrrrune claimed (recorded in ancient libraries now abandoned beneath the earth) that the ore and gem lodes would regrow if left undisturbed for long enough (one would presume this time is measured in centuries for it to be considered long to a dwarf).
Ahrrfaernd: The largest cavern in the Deep Earth is the former home of the capital of the dwarven Empire of Ahrrune (known as Dwarvenhome to the humans), and once encompassed all the territory beneath the Isles of Gwynneth and Oman.
Around -5000 DR, the cavern of Ahrrfaern split when the Quaking Chasm opened from the surface of Oman right down to the depths of the Lower Dark, causing multiple cave-ins and collapses that separated Ahrrfaernd down a fault line that extends from Oman down the middle of the Myrloch Vale and across the Corwell Firth. The formation of the Quaking Chasm shattered the strength of Ahrrune, which was later swept away by the invading duergar of Dunspeirrin.
The Underdark in this region is terrifically unstable, with magma vents and lakes throughout both halves of Ahrrfaernd around the fault line that is the Quaking Chasm. In recent centuries the Deep Earth has become more unstable and huge magma lakes and tar pools are swamping the ruins of Ahrrune and threatening the cavern roof and the surface above.
Boldokarar: This series of large caverns beneath the Isle of Norland was devastated by a series of volcanic disturbances beginning around 500 DR ending with the Rockfire Disaster of 987 DR. Much of Boldokarar is now filled with magma lakes, tar pools, or solid volcanic rock, submerging the long abandoned ruins of Ahrrune and eradicating almost any trace of that empire’s existence here.
The atmosphere in Boldokarar is hot (from the lava), and humid (from the water that pours onto the magma lakes, with gouts of super-heated steam and poisonous gasses regularly venting into the caverns and scalding anyone foolish enough to venture into Boldokarar.
Dimmeverin: This series of linked caverns is spread out beneath the Isle of Alaron.
Mycaern: This small settlement of svirfneblin lies roughly 2 miles beneath Cantrev Callidyrr. Here its inhabitants mine iron and gold and farm the great fungal forests that dominate Dimmeverin.
The people of Mycaern were once in service to the firbolgs and dwarves of the Moonshae Isles, mining the rare metals of the Deep Earth for their trading partners. When the firbolg and dwarven empires fell the svirfneblin continued their lives forgotten by everyone.
Unkoldivvern: This series of caverns is spread out beneath the Isles of Norheim and is completely separated from the caverns of Boldokarar thanks to the complete collapse of a number of caverns beneath the island of Canthrell.
Unkoldivvern was at one time the centre of industry in Ahhrune because of the stable magma flows from the lava tubes that feed Surtr’s Maw on the surface. A few dwarf holds survived the collapse of Ahrrune in secret, preserving the legacies of that fallen empire as best they could. Many of these dwarf holds were destroyed by the collapse of caverns beneath Canthrell, and the surviving dwarves were claimed by a fungal growth that was fed by the hot and humid air coming from Boldokarar.
The fungal bloom has claimed almost every cavern in Unkoldivvern, and the enormous supply of edible fungi draws creatures from neighbouring regions in the Deepshaes.
Agaric Garden: Agaric was once the centre of dwarven industry in Ahrrune, located beneath the island of Greygruun, but is now home to the largest fungal forest in the Deepshaes, with some fungus trees growing upwards of 20 ft tall. Every surface is carpeted in a thick blanket of spongy fungus that has rotted away even the sturdy dwarven constructions that surrounded the magma flows.
The fungal forest is tended by a meld of fungus people that are often confused with myconids by observing foreigners, but which in reality are the transformed remnants of the few surviving dwarves whose system was infested with a symbiotic fungus.
A colony of stirge some 300 strong also swarms about the caverns of Unkoldivvern (spending most of their time in the Agaric Garden) looking for intruding Underdark denizens that come here foraging for food. The stirges drain the intruders dry and leave the corpses for the caretakers to use to grow more fungus trees. The stirges appear to leave the caretakers alone, probably because they find the spores infesting their blood to be poisonous or unpalatable.
Humanoids that spend too long in the Agaric Garden may find themselves infected with the same symbiotic fungus as the caretakers and eventually are transformed and become caretakers themselves.
Dai’Dak (Neutral, Dwarf – Duergar, Expert 3): Dai’Dak is the laird of Clan Norghu; a mercenary group from far off Dunspeirrin. Dai’Dak has led his warriors to the Deep Earth caverns to find survivors of Deep Shanatar, but is currently scouting out Mycaern in preparation for an attack.