Bring us out of the cold

A town in the northern borderlands survives the deep winter with heating supplied by an ancient magical furnace deep under the town. Through decades of complacency and incompetence the town has lost the knowledge of how the furnace works, and haven’t even visited in decades. But winter is coming and the heat is no longer flowing.

Overview

The secret is that 200 years ago, an Efreeti was captured and imprisoned in a magical crystal at the base of this dungeon. The heat from the Efreeti is channeled up through a large pipe that runs from floor to ceiling on each level. Recently, a tribe of Grimlocks set up a Rust Monster farm on one of the floors, and the damage that the Rust Monsters have done has dislodged the crystal prison, allowing the Efreeti to partially escape.

Locations

1. First Level
   A small tribe of Goblins has set up a hot-baths service powered by the excess heat from the furnace pipe. They’ve blocked the stairs upward with debris and are charging visiting Goblins through an entrance cave that leads underground, then out into the forest outside the town.
   1. The Goblins aren’t keen to fight the players, as they feel they’ve found a profitable venture charging for the baths.
   2. The Goblin Boss just lounges in the hot bath. He’ll try to strike a deal with the players to leave them be—offering them the key to the stairs down in exchange for the players’ discretion.
2. Second Level
   This floor has four large water tanks connected to the main heat pipe by a series of smaller pipes running across the ceiling. None of the tanks are in good condition, and any players who fail a DC12 Dexterity saving throw as they walk past will be hit by a burst of boiling steam for 1d6 fire damage.
3. Grimlock Floors
   Two Grimlocks guard this area; they lurk in the southern space, playing a game that involves tossing small rocks at each other.
4. Rust Monster Farm. Two Rust Monsters are shut inside this room. If someone enters carrying iron weapons or armor, they are immediately rushed by the Rust Monsters, who haven’t been fed yet. The room is covered in debris from their feeding on iron pipes and tanks that once helped heat the town.
5. This cave is the entrance/exit that the Grimlocks use to reach the rest of their community in the Underdark (or another cave system). If the players begin exploring in this direction, they encounter a couple more Grimlocks who try to drive them back into the main dungeon.
6. Upper Floor of the Furnace Chamber
   The players will find the Grimlock Chief (use the Berserker stat block) here, with two Grimlock guards and his Rust Monster pet. The Chief orders the Rust Monster to rust holes in the tanks, which spurt 15-foot cones of steam dealing 1d6 fire damage to the players. If the players retreat onto the gantries around the furnace, the Rust Monster destroys the supports, causing the gantries to collapse and dropping the players 20 feet onto the ground below.
7. The Furnace
   This is a huge iron chamber standing free in the center. Its door is sealed shut. You could use arcane lock to make players’ lives more difficult; otherwise, it’s just locked but can be easily opened from the outside. Around the chamber are tools and workbenches once used by maintenance crews. The Grimlocks avoid going near the furnace chamber itself, so the Rust Monsters haven’t been able to damage it.
   
   From behind the iron walls of the furnace, the players can hear animalistic roars of anger.
   
8. Inside the Furnace
   This is a plain iron room. A wrought-iron frame has been knocked aside, spilling a huge cut crystal about two feet across. Materializing out of the top of the crystal is the head, upper torso, and right arm of an Efreeti. When he sees the players, he begs them to free him, explaining that he was captured and imprisoned by a wizard 200 years ago (though he omits why the wizard felt it necessary).
   
   If the players delay, he becomes extremely angry and threatens to curse them for all eternity if they don’t free him immediately, invoking his nobility in the City of Brass.
   
   Once he’s angry, it’s easy for the players to get him to admit the terrors he caused in his past life, which led to his imprisonment.
   
   The players simply need to pull him free of his prison to release him. To imprison him again, they must reset the crystal upright on its stand. Doing so restores the town’s heating supply. While the players are trying to reset the crystal, the Efreeti will attack them from his restrained position. As soon as the crystal is set upright on the stand, he is re-absorbed.
   
   The players face a quandary: free the Efreeti, who claims he was innocently imprisoned (destroying the town’s heating supply), or lock him away for another 200 years.