Mulbind-Fel is a massive hole that descends deep into the bowels of Bal-Kriav. The bottom of Mulbind-Fel is eight miles down. The mouth of the sink-hole is two miles across, and the slopes leading to the drop into darkness is a mile long. The place was named by the Mîmêk of Molcombur. These dwarves dwell deep in this Underdark abyss.

Controlling the perimeter of this sink-hole are the evil dwarves of Rethmorg. They claim that the sink-hole leads to the deepest recesses of the Underdark, and to the heart of Tarâk's realm. The upper areas of the sink-hole are laced with copper and coal mines. A massive assortment of cranes, elevators, catwalks, bridges and other structures surround the hole. Excess fresh water, sewage spillways, sludge from blacksmithing, and trash from the looming walls of Ilbaragûn are constantly being dumped into Mulbind-Fel.

Inside the sink-hole are numerous caves. Bands of Mîmêk, goblins, and other Underdark creatures live within its depths. The strongest make their way in these areas, while the weaker are pressed into slavery by both Rethmorg and Molcombur. In times of war with the Ogre Union, the Rethmorg employ these same creatures as mercenaries.