UnderRealmSetting

I should note that this section partly reveals the inspiration and physical science of what i believe the caverns are the result of, which the inhabitants of the caves due to the lack of scientific thought, may have no idea about. In many places, liberties are taken with the science.

Geology

The UnderRealm is a series of caverns, tunnels that stretches for untold thousands of kilometers. Caverns vary considerably in size, the middle and most common size is about several kilometers in diameter. Many caverns are formed in limestone, but other rock types include chalk, dolomite, marble and salt.

The second most form of cavern and one that dominates in many areas, are lava caves. These are the result of long-drained lava flows and form tunnels and large caves with relatively smoother walls than that seen in solutional limestone caverns. The rock of these caverns in primarily granite, Gabbro and other itrusive igneous rocks.

Flora and Fauna

Goop

The most basic form of life in the caverns is bacteria. Known as goop, the bacteria feeds on thousands of tiny fissures that leak warm mineral rich water located in many caverns of all types. It forms a thick biofilm of slime about 20 centimeters in thickness on average. The dominant form of bacteria is perfectly harmless to humanoids and its strong antibiotic action has effectively eliminated the competition in the caverns it is found. Goop is bioluminscent and generally a light blue in color.

Goop is also the staple foodsource for humanoids, the top layer can be easily scrapped off every few weeks and mixed with basic plants to create a fairly palatable porridge.

Flora

Without access to sunlight, plants relies on the bacteria in order to fuel their cells. Plantlife has a symbotic relationship with the goop, helping to stabilize the biofilm and draw up water.

Fauna