Umbral City of Idbëk

The Umbral City of Idbëk (/ɪ.'d͡bɤk/, lit. last capital. From i (lit. last, newest) + dbok (lit. large city, capital)) is an enormous urban complex lodged deep within the wall in atria. These atria open in the northeast of the largest Sipid Island, often referred to by the locals crudely as the Idbëk's Courtyard. Beyond Idbëk are a series of abandoned and sealed atria known as the Forsaken Atrium Complex. Few dare to even mention them, let alone explore. Idbëk is the hegemon of the Sipid Islands, taxing their thallassic vassals for food, prisoners, and alchemical ingredients.

Belief System
Idbëk's national religion is one of fungal reverence, likely originating in the inseperability between the Idbëkian civilization and the cultivation of fungus. Idbëkites believe that the sunpire is a colossal bioluminescent fruiting body of the world, which is believed to be a tangle of mycelium.

Despite this, Idbëkites pay little attention to the sunspire for its warmth is so far distant. They instead worship the Idbëk Fungal Superorganism, a fungal holobiont with hyphae that reach to the furthest ends of the Idbëk's Courtyard deep underground. Idbëkites believe themselves to be made by the IFS, a half truth; the IFS is indeed capable of making lichen bodies for Idbëkite mycopaths to temporarily inhabit.

Beyond this, the IFS makes a number of other materials for Idbëk, from bioplastics, to leather, to cloth. A special caste of worker-clergymen seek out biotic debris and collect the city's waste to be fed to the IFS.

Idbëkites feed their dead to the IFS, an act said to bring them back to their nourishing roots. The souls of the dead are believed to live and remain within the IFS, and thus Idbëkites tend to it with the utmost care and discretion.

Mycopathy
Idbëkites can practice mycopathy by connecting their nervous system with the hyphae of the IFS. This allows them to perceive things through the sensory organs of anything else linked to the fungal superorganism. Long term exposure results in a user no longer able to 'tap-out', and joins a 'hive mind' of the fungal superorganism. Mycopathy is reserved only for the high class and deemed a sacred art.

The radical wing of Idbëk's mycelial church argues for permanently integrating the entirety of Idbëk into the fungal superorganism. As a result, they are cast out, deemed heretical, and killed on sight by the classist elite. They find refuge in North Adustia, plotting revenge.

Forsaken Atrium Complex
Idbëk is the oldest continuous civilization to still exist, but it is the youngest of the nations which once inhabited the trans-Idbëkian atria. Something truly horrific happened there in times uncountable, making their mere mention an extreme taboo, fit for execution. Idbëkites have continuously fortified the corridors leading from Idbëk to the forsaken atria for thousands of generations, preparing for a threat whose form they have forgotten.

Agriculture
Idbëk primarily farms detritivorous fungus and lichen. To feed them, they collect biotic detritus from the skysea. However, most of Idbëk's food is produced in the rest of the Sipid Islands where it is then dried and shipped..

Technology
Idbëk is one of the only civilizations to extract wall material, using domesticated eusocial shipworms to dig further into the wall and molding wall fragments using the powerful enzymatic ability of the IFS. Idbëkian soldiers are therefore by far the most well armed in their sphere of influence, capable of enforcing tribute on Idbëk's vassals. Wall materials are exported to settlements closer to the sunspire in northern Phthorea and eastern North Adustia.

Idbëk is also the first civilization to achieve industrialization, using the mycosynthesis derived from the IFS to make a variety of different fungal tools, clothes, and weapons. They use standardized and mass-produced moulds to create assembly lines.