Tol Fuin, Sindarin for "Dark Isle", was the name of one of the few areas of land that escaped the drowning of Beleriand. It originally was part of the land of Taur-nu-Fuin. When the world was changed, its highest reaches survived as one of the Western Isles.
Portrayal in adaptations
Though Tol Fuin is not depicted in any of Tolkien's currently published literature, it has been shown in other media, including the map for the Middle-earth Role Playing game, as well as in one of the maps released in conjunction with Amazon's television series.