The term Darkhold does not apply to a specific country or even a city for that matter. Rather, it is the colloquial expression that describes the vast region of tunnels, caverns and caves deep below the ground that link to form a seemingly endless maze network scattered at different depths of Hyerune. Sometimes called the "Endless Deeps," Darkhold can be entered through multiple gateways located at the surface.
In general, the lands of Darkhold are not for the feint of heart. Although a few good-aligned species call the area home, the majority of the residents tent to follow more neutral or evil alignments. These include the dark elves, the mind flayers, the duergar, the derro, aboliths and the kuo-toa. Many a brave adventurer, however, will journey down into the depths of Darkhold in order to achieve fame and fortune or perhaps right some perceived wrong. Greed of course is also a strong motivating factor since many of the inhabitants of Darkhold communities trade with merchants from the surface world for commodities not native to the other. It is therefore quite possible to grow rich in the trading markets if one is brave enough to face the many potential dangers lurking in the endless tunnels.
In general, the region of Darkhold is an untamed, vast wilderness. A sea of stone and minerals under a blanket of endless darkness. If one is to hope to survive, it is necessary to unite into large communities in order to pool one's resources and strengthen a common defense. All of the more intelligent creatures of Darkhold have come together to form large city-states or kingdoms under various degrees of government and rulership. Even the most chaotic races such as the dark elves recognize the simple fact that 'freedom of the individual' does not always apply to this dark domain. Anarchy does not tend to foster survival in such a hostile world where the strong constantly prey upon the weak. The twisting tunnels and multitude of cave complexes are home to all manner of creatures such as hook horrors, gelantinous cubes, ghastly undead, grimlocks, carrion crawlers, basilisks, deadly fungi, spiders, umber hulks and countless other nightmares. With all of these potential enemies about, one must unify into large numbers or die.
The great layer of rock that forms around the region of Darkhold is anywhere from five miles thick under the ocean floor to over twenty miles thick under the three great continents. Comprised of igneous, sedimentary and metamorphic rocks, the whole structure is primarily composed of silicon and oxygen along with a few other common chemicals. Deposits of iron and other metals can be found scattered throughout Darkhold which of course is ideal to the many mining races that call this area home. The whole structure itself is under a constant state of flux as the rock slowly heats up over time from the tremendous heat that radiates from deep in the planet's core, rises toward the surface, cools and sinks back toward the planetary mantle. This "current" of rock is so slow and subtle of course that it is basically unnoticable but can account for shifting tunnels and caverns over time. Deep underground tremors and quakes also greatly affect this formation.
Explorers to this region must be constantly aware of the many natural dangers found in the Darkhold in addition to the sentient beasts that dwell here. Layers of molten rock, hot springs, fissures, lava tubes, geothermal heat and even poisonous gases can prove quite deadly to those inexperienced to the ways of life in the underground world.
While visiting the vast region of Darkhold, be sure to check out some of these main tourist attractions:
Cyrth-Aglin
The dark elven 'Venice,' the City of Cyrth-Aglin is located on a large, rocky island on a wide underground sea. The island is laced with multiple canals and boat traffic is just as common as street walkers. It is said that the unhallowed shores of the island are guarded by dark elven merfolk allied with the ruling council fo Sheolban priestesses.
Drugathzha
The slave-city of the mind flayers and one of the most remote regions of Darkhold. The city is built upon the blood of countless slaves under the mental control of the mind flayers and surrounds a great orb of ectoplasm said to be a conduit into the Astral Plane. Powerful clerics of Amygdala, the mind-flayer goddess, hold much influence in the city and even attempted a recent but failed coup.
Morthindhol
The City of Gloom, Morthindhol is the largest and most powerful city of the dark elves on Hyerune. It is controlled by the Ennead, nine clerical noble houses of the dark elf goddess Sheolba. It is a shadowly faerie-land of stone and crystal spires located near an enormous fungal forest.
Nun'Oolra
The dark elven term for 'Dark Abyss' describes this city perfectly. It consists of a great cavern at the lowest point within the world's crust and is a region of perpetual darkness. Unlike other dark elf cities, however, Nun'Oolra is controlled by opposing factions with the female priestess of Sheolba against the male rogues and sorcerers of the Thieve's Guild. The two constantly strive to undermine or depose of the other in order to rise to preeminace within the city hierarchy.
Sunless Sea
An immense underground sea contained within a vast cavern many thousands of miles in length. Its chilling waters are home to many aquatic creatures both malevolent and benign as well as a species of cave fish native to the area. It is rumored to also contain the ruins of a former abolith empire as well as a thriving kuo-toa spawning bed.
Thorandor
A mighty clerical kingdom of the black dwarves located deep under the Spineridge Mountains of Northern Aldaria. The dwarf city is legendary for its great wealth and highly skilled armorers and craftsmen. It is a holy place dedicated to Denethor, the chief dwarf deity, whose clerics are highly influential in affairs of state.
Zhedek Cha
The ancient home of the derro, the name means 'Veiled City' in the Derro tongue. It takes the form of a massive series of step layers that unite to form an inverted ziggurat. The city itself is quite difficult to find as it is cloaked in potent spells of invisibility and illusion. The deepest levels of the ziggurat are said to contain the palacial estate of the powerful derro-king and can only be reached by making ones way down layer after layer.