The Forge of Muspar

The volcano smokes differently than it should: rhythmically, like a panting bellows. In the mountain villages they know why. Deep in the throat of the mountain, the fire giant Muspar the Smith has built a forge, and on his anvil grows a weapon that can melt away entire city walls, ordered by a warlord who means to subjugate the whole land.

Slaves haul ore along glowing channels, lava streams through cast troughs, and the heat alone kills the unprepared. Muspar counts the days until the weapon-melt is complete; you count them with him, because when it is finished, every wall between here and the capital is lost.

You creep through lava tunnels, foul up the bellows and the water supply, free slaves who know the mines, and search for the weak spot in Muspar's masterwork while it is still glowing and unfinished. Every act of sabotage makes the smith more suspicious and the Forge of Muspar more dangerous.

The twist: the warlord holds Muspar's daughter hostage, and the giant forges not out of pride but under duress. The climax plays out on the rim of the crucible: destroy the weapon in a battle against Muspar the Smith and his heat, or convince him that you can free his daughter and turn his hammer against his employer, before the lava rises and the whole forge plunges into the deep.