| Category | Caverns |
| Continent | Brucrumus |
| Region | Unaraggumak |
| Map | Khelan |
The great Atharâg river once had a tributary that flowed through this region. Fungal growth originating from Crulock began obstructing the western flow around the beginning of the Lith-Crillion Era. This magically amplified vegetation proliferated rapidly, expanding eastward along the river banks and into the waterway itself. By the end of the era, it had forced the tributary to carve a new course, doubling back to its source forty miles to the north and east. The fungal growths were halted by this change in flow, now forming a vast semicircle of powerful water movement. The strength of the current is such that it tears apart any vegetation attempting to take hold, which is further combated by a group of druids serving the Nature Protectorates. This organization views the magically enhanced flora as a threat to the area and is charged with containing it within the Mephirouth Trench.
There is a diverse array of Underdark vegetation lining the dried riverbed, its banks, and the vast cavern at its center. Most of these plants are harmless. However, the dangerous varieties include gas spores, phantom fungus, shambling mounds, tendriculos, yellow musk creepers, snapper saws, strangle vines, and a host of other predatory plant life. The verdant Fungals of Mephirouth Trench also serve as a habitat for creatures that feed on the plants, such as giant beetles, flies, centipedes, and their own predators, forming a complex Underdark food chain.
The Myconids also have a substantial presence in this region. They are dispersed and in small groups numbering in the thousands. An expedition into the interior by Aredhel, prior to her ascension to divinity, revealed that these groups remain small and scattered due to something called the Mephirouth Rot. This plant disease is named after the primordial Mephirouth who once resided at Crulock. The Mephirouth Rot gradually causes the brains of sentient plants to decay, resulting in insanity and, for some, a permanent confusion akin to the wizard spell of the same name. After several large colonies were decimated by this affliction, the local myconids opted to maintain their populations in a small, dispersed manner. Occasionally, they convene and eradicate thriving colonies, often enlisting the aid of outside mercenaries such as fire mages and pyromancers.