Mirror of Galadriel
The Mirror of Galadriel is a basin filled with water in which one may see visions of the past, present and future. Galadriel, an Elf Lady in the woods of Lothlórien, invites the story's hero, Frodo Baggins, to look into it. Galadriel cannot predict what the mirror will show and does not guarantee that its visions will come to pass.
Samwise Gamgee was also allowed a vision, which turned out to be a choice between returning to the Shire to prevent its destruction by technology or to continue on the quest with his master to prevent Sauron from destroying all of Middle-earth.
This recalls the ancient practice of water scrying or hydromancy: gazing into a shallow pool or bowl for purposes of divination. The Norns of Norse mythology used the Well of Urd as a scrying bowl.