Oh, there's one additional thing I forgot to mention from Die Nibelungen.
As a condition for allowing Siegfried to wed Kriemhild, her brother Gunther asks Siegfried to help him win the hand of the fierce warrior woman Brunhild. Brunhild lives in far-off Iceland, in a castle on a high rock that is surrounded by a sea of fire.
The flames are prophesied to quench themselves at the approach of the world's mightiest warrior--and they do, as Siegfried approaches the castle.
This image is an obvious inspiration for Lucas's idea, seen in the first draft of ESB, that Darth Vader would live in a castle on a tall mountain surrounded by a sea of lava.
In the notes for the Journal of the Whills outline, Lucas's use of the names "Yoshiro" and "Brunhuld" as, respectively, the names of the good guys' and bad guys' planets (later to become Aquilae and Alderaan in the rough draft) is quite reflective of the sources these two names are derived from. Toshiro Mifune is a hero in Seven Samurai and Yojimbo; Brunhild is (in Fritz Lang's film, at least) portrayed as a villain.