Send Valbullion?
The Forbidding Hills were the site of a great battle between man and beast. The tower positioned in the hills for the purposes of national security was quickly overrun. 15,000 men died that day, and those numbers plus a few thousand mere were the casualties that the enemy faced. The beasts came through the hills, surrounded the tower and slaughtered everyone there without any known provocation or reason.
The ruined remains of the tower have been turned into a barrow and the hills are the site of a mass grave holding those 15,000 men; the corpses of the beasts were burned to ashes, given no rites or prayers, and forgotten forever. These hills are riddled with potent negative energy. Spirits and poltergeists, some mere death echoes while others are malignant manifestations from soldiers who died with much hate in their heart, float around the hills, buzzing in and out of existence randomly and saturating the area with ectoplasm.
The hills had become a necropolis. In the next one hundred years or so, perhaps a consequence of a society attempting to suppress so grave a recollection, the memory of what travesties had taken place on the grassy hillocks was forgotten. From then on, the hills were treated with unease and anxiety. Few made it a point to travel there, and roaming caravans steered clear of the boundaries of the Forbidding Hills without knowing exactly why their hearts filled with dread.
It wasn't until the mystic sage Herbie discovered the long-forgotten truth of the Forbidding Hills that passage around and through them became a commonality and the people learned to apply cold logic to their fear. Since those 500 years of yore, the memory has faded once again and the general aura of blight and blasphemy has yet to dim.
Rumor has it that this dark aura is used as cover by the Drow, and that an entrance to one of their three remaining subterranean cities lies somewhere among the profane landscape.
Canon
1. (No ST). The necromancer Alexander resurrected the 15, 000 dead soldiers of lore and stormed the drow city hidden beneath the hills. After being slaughtered, they too were resurrected and used to build a fortress surrounding the old tower. The hills have since been turned into a wasteland and home for all kinds of evil creatures, and Alexander has renamed the land Arnim Tor.