When triggered, the floor begins rapidly moving forward like a magical conveyor belt, and a gate or hatch opens on the far end, revealing an active blast furnace. Characters have only 1 to 2 minutes (50-50% chance) to figure something out, or be incinerated.
Characters ending up in the furnace take 5d6 HP damage per minute. The conveyor runs for three minutes, after which it stops, and the door to the furnace gate closes. The fire in the furnace is magical, however, and continues to burn, whether the door is open or not. Characters inside or out (who are still alive) must make a successful Strength roll or Saving Throw to lift the gate.
Optional: There may chandeliers on the ceiling, carvings on the wall, steam pipes overhead, etc. to try and grab hold of before going into the furnace (successful Dex roll or Saving throw).
Optional: The conveyor can be jammed with a metal blade, arrow tip, etc., if successfully hit in the right spot (roll to hit AC equivalent of a bullseye).
Fernbrake by YearOfGlad. Modified by David in Inkscape. Creative Commons Attribution-Share Alike 3.0 Unported.