Before people start believing new myths: this story has nothing to do with Odin. Its source is probably Grimm's Tales (1819), whose editors attribute it to a Bavarian collector.

Notably, the mountain is far away, but on the solid ground of 19th century physics: it has three dimensions and is made of diamond, by then known to be the hardest mineral in existence.

Nevertheless, we hear the ancient universal tradition of riddle stories.

The song by an American songwriter falls somewhat short of that. "Ten thousand miles square" sounds wrong altogether, for sake of rhyme. Worse, a supernatural setting is chosen, thus the point is missed.