Firewater

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.