You find a box in the attic.
This box contains a cup on a stand above lit candle. The cup holds a “flame” whose tongues are made of water moving as a real flame would move. Pouring this water into another body of water will cause that body of water to erupt into the same kind of fire-like motion. This “fire” is endothermic. When the water cools to freezing, the motion ceases, leaving an ice sculpture of roiling fire.