Aman, the lands in the Ancient West (somewhat conjectural)

A name for the lands that lay beyond the Great Sea, otherwise known as Aman, the Blessed Realm where the Valar and the Maiar dwelt, and where many of the Eldar later settled to dwell in bliss beside the Powers. During the First Age and most of the Second, the West was part of the world, and could even - in exceptional circumstances - be reached by ship. After the founding of Númenor, the Valar placed a Ban on the Númenóreans from sailing there, fearing that they would be tempted by the bliss of the Undying Lands, and that fear proved well-founded.

In II 3319 King Ar-Pharazôn led a great fleet from Númenor that broke the Ban and attempted the conquest of the West. He failed utterly, and brought about the Downfall of his own realm, but at the same time the lands of the West were taken away from the world, and after that time only the Eldar could travel the Straight Way and come there. By the time of the War of the Ring, the lands of Aman - by that time the Ancient West - had been lost to Mortals for more than three thousand years. Even at that time, certain Mortals were granted the special blessing of being allowed to travel there, notably Bilbo and Frodo Baggins.