The young man first visited France. He was served escargot, to his horror, and was left with a poor impression of the French. He moved on to Germany, taking a boat down the Rhine River (which he thought smelled like a tremendous fart), until he arrived in a small town called Isenstein. While eating in a pub, he met Regin Fafnirsbruder, who thought the young man's name sounded like Hagen Kriemheld. He lured the young man out of the town, and then magically transported them both into the past.
The young man barely understood what had happened to him, and was even more astonished when Regin Fafnirsbruder brought him to a castle surrounded by a ring of fire. Regin insisted that the young man cross the ring, enter the castle, and awake Brunhild, a woman imprisoned in the castle. The young man began to berate Regin, who responded by shoving the young man through the fire. The young man was unhurt, but when he tried to walk back out, he nearly burned himself. Seeing no choice, the young man entered the castle, and discovered Brunhild, slumbering in armor. He gave her a quick peck on the cheek, which woke her. At first, she was disappointed that the young man was not her true love, Siegfried, but was prepared to honor the terms of the enchantment, which required her to marry the soul who could cross the flame.
The young man introduced himself (Brunhild also thought his name was Hagen Kriemheld), and explained how Regin Fafnirsbruder had brought him to the castle. Understanding that both of them had been victims of Regin's trickery, Brunhild rushed from the castle, the young man close behind, and sought to kill Regin, but he vanished before her sword could strike home. Brunhild then turned back to to the young man, and again stated that she would be his. Sensing that Brunhild would only hate him if he took her as his bride, the young man refused, allowing her to return to the castle. She quickly saluted him with her sword, gave him a chaste kiss and rushed back to the castle. Wanting a more passionate encounter, the young man tried to chase after her, but, as he was no longer immune to the fire, he nearly burned himself instead.
Trapped in the past, the young man went back to Isenstein. He was not versed in Norse or German mythology, and so did not fully understand the importance of Regin or Brunhild, or why the fact their belief that his name was "Hagen Kriemheld" was so important. He had no skills useful in an early Medieval society and no assets other than modern paper money and travelers' checks, utterly worthless in the past - and, moreover, he had not been very successful even in the society into which he was born. 
While "Hagen Kriemheld's" true name is never explicitly stated, it is understood that he is Holden Caulfield, the narrator of the novel Catcher in the Rye (1951) by J.D. Salinger (1919-2010).
Kriemheld is a woman in the Nibelungenlied, who pined for Siegfried while the latter only had eyes for Brunhild.