The Palantír of Elostirion was one of the Palantíri, stored in Elostirion. It was aligned westwards, along the length of the Straight Road and could only be used to look west across the sea, to allow Elendil to see the Undying Lands.
It was also used by Wandering Companies to catch a glimp of Varda. One such company, led by Gildor Inglorion, was encountered by Frodo and Sam in September T.A. 3018. They had just returned from Elostirion.