Inanweg is a vast labyrinth beneath the Mauhúlfúr valley. It was created from the linking of many of Mauhúlfúr's barrow; each a mini-labyrinth to deter grave robbers. The linking of the first pair of barrows began in the First Epoch when a cult of demon worshipers tunneled into the Barrow of Khadon (c.f. Ogre Lords). They came up from underneath, following a passage bored out by a Scion of Krephus. The cultists worshiped Juiblex and for a time lay claim to two of Mauhúlfúr sub-surface barrow labyrinths. They connected these two with subterranean passages. When Gúra learned of the cultists digging in the barrows of their Ogre Lords, they sent an army to root them out. They destroyed the cultists and their temple. Since that time, other barrows have been connected from underneath out of accident or desire to expand their Underdark living space.
The ruins of the Temple of Juiblex are still a problem for both the surface and underneath. Periodically, the altar in this place spews forth giant slugs and black puddings. These creatures can be found in high numbers across Mauhúlfúr and in the subterranean complex Inanweg beneath it.