Númenor is the fictional island kingdom that sinks in J.R.R. Tolkien’s history of Middle-earth.
Númenor is an island realm granted to the Men who aided the Valar and Elves during the war against Morgoth. Its people receive long life and great knowledge, but they are forbidden to sail to the Undying Lands in the west. Over time, fear of death and resentment toward the immortal beings contribute to Númenor’s downfall.
King Ar-Pharazôn is deceived by Sauron and attacks the Undying Lands. In Tolkien’s account, Eru Ilúvatar changes the world, the island is overwhelmed, and Númenor is destroyed. The survivors led by Elendil establish realms in Middle-earth, including Gondor and Arnor. Valinor is the realm in the west, not the island that sinks.