Odin is the "boss god" in Nordic and Germanic mythology. The "Big Kahuna."   He rules over such places as Valhalla, a sort of "heaven" analogy, where everybody sits around enjoying themselves by drinking mead, and swapping tales of glory. Warrior maidens, riding flying horses, fly over battlefields and when they see a warrior die bravely in battle, they pick him up and carry him to Valhalla. These warrior maidens are called Valkyries.

Richard Wagner's "The Ring of the Niebelungen," four operas in series, deals with the machinations of Odin ("Wotan" in German) and his twelve Valkyrie daughters, particularly Brunnhilda, who, on one occasion, disobeys him. All of the Valkyries are Wotan's daughters, the offspring of he and Erda, the earth goddess--although Wotan's wife is Freya, the goddess of Spring.   These four operas run about twenty hours altogether. My wife and I attended Seattle Opera's "Ring Festival," all four operas within one week and wound up with our ears glowing, but badly rump-sprung!

Norse myth is a rich field that heavily influenced Germanic mythology (hence, Wagner's interest), and leaked over into Celtic myth.

The mountain in "The Land of Odin" would probably be somewhere near Valhalla, which one enters either by being carried there by a Valkyrie or by crossing over a Rainbow Bridge….

Don Firth

P. S. My guess is that J. R. R. Tolkien was strongly influenced by the Norse tales, particularly the same one that fascinated Wagner—the magical ring that grants wishes, that everyone covets, and that eventually destroys its possessor…. Just a guess, but the similarities are strikingly compelling.