Die Walküre
Wotan goes to the Valkyries.  He is furious with Brünnhilde because she disobeyed him.  He punishes her.  He tells her that she is no longer a Valkyrie.  She will fall asleep on a rock and any man who finds her can have her.  Brünnhilde pleads with Wotan.  She asks him whether he could, at least, put a fire round her so that the only man who could get her would be a hero.  In the end Wotan agrees.  Loge, the god of fire, arrives and lights the fire.  At the end of the opera Brünnhilde is asleep on the rock, surrounded by the fire.  There she will stay until, one day, a hero comes to rescue her.