Here lie the sleeping forms of Wotan, the king of the gods, and Fricka, his wife.  Behind them, upon a neighbouring mountain, rise the towers of Valhalla, Wotan’s new palace, built for him by the giants Fafner and Fasolt in order to ensure him in his sovereignty of the world.  In exchange for their labours Wotan has promised to give them Freia, the goddess of love and beauty, but he hopes by the ingenuity of Loge, the fire-god, to escape the fulfilment of his share of the contract.  While Fricka is upbraiding him for his rash promise Freia enters, pursued by the giants, who come to claim their reward.  Wotan refuses to let Freia go, and Froh and Donner come to the protection of their sister.  The giants are prepared to fight for their rights, but the entrance of Loge fortunately effects a diversion.  He has searched throughout the world for something to offer to the giants instead of the beautiful goddess, but has only brought back the news of Alberich’s treasure-trove, and his forswearing of love in order to rule the world.  The lust of power now invades the minds of the giants, and they agree to take the treasure in place of Freia, if Wotan and Loge can succeed in stealing it from Alberich.  On this quest therefore the two gods descended through a cleft in the earth to Nibelheim, the abode of the Nibelungs.  There they find Alberich, by virtue of his magic gold, lording it over his fellow-dwarfs.  He has compelled his brother Mime, the cleverest smith of them all, to fashion him a Tarnhelm, or helmet of invisibility, and the latter complains peevishly to the gods of the overbearing mastery which Alberich has established in Nibelheim.  When Alberich appears, Wotan and Loge cunningly beguile him to exhibit the powers of his new treasures.  The confiding dwarf, in order to display the quality of the Tarnhelm, first changes himself into a snake and then into a toad.  While he is in the shape of the latter, Wotan sets his foot upon him, Loge snatches the Tarnhelm from his head, and together they bind him and carry him off to the upper air.  When he has conveyed his prisoner in safety to the mountain-top, Wotan bids him summon the dwarfs to bring up his treasures from Nibelheim.  Alberich reluctantly obeys.  His treasure is torn from him, his Tarnhelm, and last of all the ring with which he hoped to rule the world.  Bereft of all, he utters a terrible curse upon the ring, vowing that it shall bring ruin and death upon every one who wears it, until it returns to its original possessor.  The giants now appear to claim their reward.  They too insist upon taking the whole treasure.  Wotan refuses to give up the ring until warned by the goddess Erda, the mother of the Fates, who rises from her subterranean cavern, that to keep it means ruin.  The ring passes to the giants, and the curse at once begins to work.  Fafner slays Fasolt in a quarrel for the gold, and carries off the treasure alone.  Throughout this scene the clouds have been gathering round the mountain-top.  Donner, the god of thunder, now ascends a cliff, and strikes the rock with his hammer.  Thunder rolls and lightning flashes, the dark clouds are dispelled, revealing a rainbow bridge thrown across the chasm, over which the gods solemnly march to Valhalla, while from far below rise the despairing cries of the Rhine-maidens lamenting their lost treasure.