His first adventure was in Isenland, or Iceland, where he broke through a magic ring of fire that for many years had burned around a lofty castle on the summit of a mountain. In this castle lay Brunhild, a disobedient Valkyr whom Odin had punished by putting her and the king and court who had received her into a sleep. This was to last till some hero should pass the ring of fire. Siegfried broke through, found the beautiful maiden, and became betrothed to her. But after a brief period of happiness Odin bade the hero leave Isenland and go elsewhere in search of adventures.

Siegfried went next to the land of Burgundy, and there he found a new exploit awaiting him. King Günther had heard of the beautiful Brunhild, and was eager to marry her. Many a man had lost his life because of this same wish; for whoever would win her must outdo her in the games, and if he failed, both he and his attendant knights were put to death. The king and Siegfried set off for Isenland, and the games began. First, Brunhild threw her heavy javelin against the king's shield; but Günther cast it back at her so powerfully that she fell to the ground. When she rose, she caught up a stone, so heavy that twelve knights could hardly lift it, and hurled it an amazing distance. Then at one leap she sprang to where the stone had fallen; but Günther threw the stone farther and leaped farther. Then the Valkyr yielded and became his wife. She did not guess that it was not Günther who had beaten her, but Siegfried. Siegfried had a magic cap of darkness, and when he put it on, he became invisible; so while Günther went through the motions, it was really Siegfried who threw the javelin and hurled the stone and even carried Günther in his arms far beyond the leap of the Valkyr. So it was that Brunhild became the wife of Günther. As for Siegfried, an enchantment had been thrown about him, and he had entirely forgotten that he had ever ridden through the ring of fire or seen Brunhild before. The hand of the king's sister, the gentle, lovely Kriemhild, was to be his reward for his service to King Günther; and now both weddings were celebrated. Günther and Brunhild remained in Burgundy, and Siegfried carried Kriemhild to his kingdom in the Jutland.

Even if Siegfried had forgotten Brunhild, she had not forgotten him, and she meant to have her revenge. She persuaded Günther to invite Siegfried and Kriemhild to Burgundy. It was easy for a quarrel to arise between the two queens, and Hagen, uncle of Kriemhild, took the part of Brunhild. He pretended that war had arisen against Günther, and Siegfried agreed to fight for his host. Kriemhild begged her uncle to help Siegfried whenever he was in peril; and the treacherous Hagen replied, "Surely; but first tell me where his chief peril lies. Is there some one way by which he may most easily lose his life?" "Yes," answered Kriemhild, "he once slew a dragon and bathed himself in its blood. Therefore no weapon can harm him save in one tiny place between his shoulders which was not touched by the blood because it was covered by a linden leaf." "Then do you sew a mark upon his garment directly over that place," said the false Hagen, "that I may guard it well." One day Siegfried went out hunting with Günther and Hagen, and it was not long before his body was brought back to the sorrowing Kriemhild. The treachery of Hagen, however, was not to be hidden, for during the funeral rites Siegfried's wounds began to bleed afresh as Hagen passed the bier; and from this Kriemhild knew that he was the murderer of her husband.

Siegfried's father lovingly begged Kriemhild to return to the Jutland with him; but she would not leave Burgundy, for she hoped some day to avenge her murdered husband. She sent for the Nibelung treasure and gave generously to all around her. Then wicked Hagen began to fear that the hearts of the people would turn towards her. Therefore he stole the treasure and sank it deep in the river Rhine; but he meant to recover it some day for himself.

It came about that King Etzel of Hungary sent a noble envoy to beg for the hand of the widowed queen. She answered him kindly, for she said to herself, "Etzel is brave and powerful, and if I wed him, I may be able some day to avenge my Siegfried." So it was that Kriemhild became the wife of Etzel, and was true and faithful to him for thirteen years. At the end of that time she asked him to invite the king and court of Burgundy to visit them. The Burgundians accepted the invitation, though the murderer Hagen urged them to remain at home. In Hungary they were treated with all courtesy; but Kriemhild had told her wrongs to her Hungarian friends, and as the guests sat at a magnificent feast given in their honour, the Hungarian knights dashed into the hall of feasting, and slew almost every one. Günther and Hagen yet lived, and Kriemhild bade Hagen reveal where he had hidden her stolen treasure. "Never, so long as Günther lives," was his reply. Kriemhild ordered Günther to be put to death and his head taken to Hagen, but Hagen still refused to tell what had become of the treasure. In her anger Kriemhild caught up the magic sword of Siegfried and struck off Hagen's head at a blow. Then one of the Burgundians cried, "Whatever may become of me, she shall gain nothing by this murderous deed"; and in a moment he had run her through with his sword. So ended the story of the treasure of the Nibelungs, which brought ill to every one who possessed it.