Based on the Advanced Dungeons & Dragons module White Plume Mountain by Lawrence Schick, HackMaster's White Doom Mountain is designed for characters level 4-7.
Excerpted from the back cover:
Just two and a half weeks ago, three extraordinarily valuable and storied weapons (each also extremely powerful) disappeared form the various places they were kept. Each of the three, cryptically known as ThumpMaster, Skewersure, and Hackrazer, vanished without a trace. All of them had been in the possession of well-known if not well-regarded individuals in and around Fangaerie. The weapons were taken despite the formidable skills of the individuals in question and the various guards and wards of their respective dwelling places.
The owners were slain, the various guardians and magical sureties left untouched and untriggered. Not even the most potent of necromantic sorceries were able to contact the departed spirits of the dead, nor could the corpses be raised or resurrected. The weapons were unexplicably and undeniably gone.
The unprecedented mystery remained a crime without a clue, until a taunting poem suddenly appeared. The rhyme materialized without witness or explanation on the walls of taverns and inns across the land, from Frandors Keep's Burning Dawg Inn to the Gilded Lily in Hesur. This poem, which seemed to create more questions than it answered, was signed with the serpentine rune of Keraptorse.
White Doom Mountain has tentatively been identified as the location spoken of in the poem. It stands forbiddingly on a small island just outside the shipping lanes of Raga, and is regarded as an unlucky and cursed place by the mariners there. A continuous plume of caustic smoke, steam and deadly white ash hangs suspended above it, and the lake surrounding it has been masked by thick mists since before living memory. To scholars, sages and pundits the place seems likely enough.