The Darklands region below the continent of Tian Xia is in some ways similar to, but in other ways very different from, that of the Inner Sea region. Like its western counterpart, the Darklands of Tian Xia are broken down into three levels, Nar-Voth, Sekamina, and Orv. What is most different are their inhabitants: these Darklands have no major populations of duergar, drow, or derro. Instead, they are home to haunted clockworks, denizens of Leng, oni, and cave giants. Greedy underworld dragons are also known to inhabit the Darklands of Tian Xia, creating their labyrinth-like lairs in its benighted depths.
The upper reaches of the Darklands of Tian Xia, much like those found elsewhere, are intermittently connected to each other and do not form a continuous network—travel from one cave complex through another often requires passage over the surface or through the deeper layers of the Darklands. The inhabitants of the Tian Xian regions of Nar-Voth include myceloids, who often raid the deeper caves of Sekamina, and a rumored nation of hobgoblins mirroring Kaoling on the surface.
The Sekamina of Tian Xia is roughly split between five areas:
- the great, spiral-shaped oni city of Shirogoku beneath Minkai
- the caverns beneath the Wall of Heaven mountains, home to cave giants, troglodytes and horrors from Leng
- the fractured and and quarrelsome ratfolk domains of Diguo-Dashu beneath the center of the continent
- Zaikongon, a realm beneath the Valashmai Jungle ruled by seugathi, brain oozes, and other such monsters
- the haunted clockwork city of Pan Majang north of Zaikongon.
Underworld dragons also live here in numbers, ruling realms between the five main nations and often manipulating their politics and workings.
The Vaults that lie beneath Tian Xia are even more mysterious and poorly explored than those beneath Avistan and northern Garund, but rumors and legends about them have percolated to the surface over time. What little is known of them speaks of realms of malformed giants, portals to nightmarish realms of the Abyss, seas of living oil, and horrors from the Dark Tapestry waiting in their dark depths.