It is far from clear what happened to the Walls of Night after the cataclysm that destroyed Númenor and changed the shape of the world. We can be sure that the Walls existed during the Second Age (we have a description of Númenórean explorers finding their way to the Gates of Morning in the distant East). After the world was made round, however, there could be no possible place for the Walls to stand (and so from a mortal perspective, they would essentially have ceased to exist). The Elves, however, could still travel the Straight Road into the West, and so from their perspective the Walls may have remained in place, at least after they left the Bent World behind them.

The map shown here combines elements from sketch maps by Tolkien that are reproduced in volume IV of The History of Middle-earth. These original sketches are the only maps we have showing the entirety of the world as he conceived it. They are, however, rather rough in nature, and belong to a very early phase of Tolkien's work, so they cannot be expected to fit fully with the geography of the world as it was later worked out. For further details, see footnote 1 to the entry for Arda.