From Tolkien Gateway
Tol Uinen was a small island that stood off the coasts of Númenor, in the long narrow bay of Rómenna that separated the regions of Orrostar and Hyarrostar. Legend said that the island had been placed there by Uinen herself, the Lady of the Seas, who was held in particular reverence by the mariners of Númenor. Indeed, the Guild of Venturers called themselves Uinendili - devotees of Uinen - and often moored their great ship Eämbar off Tol Uinen. Their Great Captain, Aldarion, raised a tower on the island named Calmindon, to shine a light across the waters of the bay of Rómenna.