The Volcanic Vault of the Forge Father

From the introduction:

In ages long past, the Dwarven Sorcerer-Priest Hargen the Seven-Crowned stole a fragment of the Elemental Plane of Fire. Using this stolen power, he built a hidden vault deep within the earth. A volcano formed around the Shard, and in his volcanic vault, he forged many great and terrible weapons, to war with the Gods themselves. However, exposure to the raw power of the Fire Shard corrupted the dwarves, twisting them into ferocious Ash Ghouls. With the last of his power, Hargen sealed the vaults. However, recent volcanic activity has caused the tunnels to reopen, and eager adventurers are taking the opportunity to plunder its depths before it is drowned in lava.