After the fall of Númenor, the world was bent, so that the Undying Lands lay no longer on the mortal plane, as their promise of living forever was too great a temptation for Men to bear, and the attack on them by the King of Westernesse proved that the old proscriptions no longer held sway in the hearts of Men. The Elves still posess the ability to sail to them, however, and it is to these lands that the Sea-Elves that Frodo meets early in his journey are travelling, and to which all Elves eventually will go. go.
