You can supercool hot ice or sodium acetate so that it will remain a liquid below its melting point. You can trigger crystallization on command, forming sculptures as the liquid solidifies. The reaction is exothermic so heat is generated by the hot ice.
You can make your own sodium acetate or hot ice and then cause it to crystallize from a liquid into ice while you watch. The solidification generates heat, so to the casual observer it's as if you're turning water into hot ice.