Underdark

The Underdark is a vast subterranean network of caverns and tunnels that spans the entire underground of the world of Infinity Seed, expanding so deep that some of the furthest reaching tunnels emerge under the world and are exposed to the great emptiness.

Entire empires rise and fall within the caverns of the Underdark, and the realms of the demons and devils lay deep within the bowls of the world, as well as the realms of some gods.

Layers of the Underdark
Within the Underdark are a multitude of layers. The uppermost layers consist of the cavern and tunnel systems that are only up to 5 miles beneath the surface. These layers house races who usually live on or close to the surface world, such as Dwarves and Kobolds. Many kinds of Dragons will only make their lairs within this layer of the Underdark, and no deeper. It takes 1,600 years for the Underdark to grow 5 miles thick.

The second layer stretches from 5 miles to 15 miles beneath the surface. Very few races who are comfortable on the surface will dare to venture deeper than this. This layer is where most of the larger settlements of Underdark dwelling races are, including Drow cities. Underdark dwelling monsters are often found here too, and most of the dragons who prefer to dwell in the Underdark live here. The realms of several deities can also be found here. It takes 4,800 years for the Underdark to grow 15 miles thick.

From 15 to 30 miles beneath the surface, the Underdark becomes a very isolated place. Caverns are less common, except where powerful beings have already staked their claim. Most of the demon and devil realms are found in this layer, as are a few deities. Very few mortal races choose to settle so far down. It takes 9,600 years for the Underdark to grow 30 miles thick.

Between 30 and 50 miles deep is where the major "hells" are, the domains of the most powerful demon princes and devils. Lakes and rivers of lava are common, and almost no mortals are found alive. Truly ancient beings can be found chained in this layer, but only closer to the world's center, where it is deepest. It takes 16,000 years for the Underdark to grow 50 miles thick.

Underdark that is deeper than 50 miles only occurs towards the world's center, and much of it is completely unoccupied. In its lowest reaches you can find unfinished tunnels that open out into the emptiness. This layer can keep growing forever. It takes 32,000 years for the Underdark to grow to 100 miles thick for example.