Mime tells his foster son Siegfried that he is not his real father. He shows Siegfried the shattered sword Notung, which is beyond repair. Once Siegfried has left, the Wanderer enters and tells Mime that Notung can only be forged anew by someone who fears nothing.
As Siegfried returns, Mime attempts to find out whether he could be fearless enough. Mime comes up with horrific scenarios, but Siegfried just laughs at them all. He smashes the fragments of the sword and manages to reforge Notung. Meanwhile, Mime prepares a poisonous drink meant for Siegfried. Both now head towards Fafner’s cave.
Alberich is standing guard near the cave, at loss at how he could get the treasure he so desires. When he sees the Wanderer, Alberich recognises Wotan. Wotan tells him that the hero capable of killing Fafner is about to arrive, but that Mime is after the treasure. Wotan wakes up Fafner to warn him. Alberich repeats his demands to rule the world and stays to witness the arrival of Siegfried and Mime.
Siegfried is listening to the birds and tries to call back to them with a reed pipe and a silver hunting horn. The horn wakes up Fafner, and in the ensuing battle Siegfried strikes Notung into the monster’s heart. The dying Fafner warns Siegfried about the future. Fafner’s blood makes Siegfried understand the language of birds, who tell him to take the ring and the magic helmet and to watch out for Mime’s devious plans. Mime tries to get Siegfried to drink the poison, but Siegfried grabs his sword and Mime’s dead body soon lies next to Fafner’s. The forest birds tell Siegfried of a woman surrounded by fire on a rock, who is waiting for her saviour.
Wotan summons Erda to find out whether his plans will come to fruition. Erda bids Wotan to seek the advice of the Norns. Devastated to hear about her daughter’s punishment, she then resumes her eternal sleep.
As Wotan tries to bar Siegfried’s way to Brünnhilde’s rock, Siegfried uses Notung to break Wotan’s spear, which once shattered that very sword. The god steps aside and allows the young man to continue on his journey.
Siegfried pushes through the flames and finds a sleeping hero, who turns out to be a woman. He hopes to have found his long lost mother, but Brünnhilde tells him his mother is dead. At first she resists his advances, believing that her saviour should retain his innocence, but eventually she can’t control her emotions. Fuelled by the fervour of love, Siegfried and Brünnhilde demand the destruction of Valhalla and the gods. Enraptured, they hail ”light-bringing love and laughing death”.