Númenor is a fictional island kingdom from J.R.R. Tolkien's legendarium, primarily featured in "The Silmarillion." It was located in the Great Sea, between the continents of Middle-earth and Aman. Founded by the Dúnedain, descendants of the Edain, Númenor was known for its advanced culture, impressive architecture, and long-lived inhabitants. The island was shaped like a star and had a rich history, marked by the rise and fall of its kings. Eventually, Númenor fell into decline due to the influence of Sauron and the desire for immortality, leading to its catastrophic downfall and submersion in the ocean.