'Turning aside, she led them towards the southern slopes of the hill of Caras Galadhon, and passing through a high green hedge they came into an enclosed garden. No trees grew there, and it lay open to the sky. The evening star had risen and was shining with white fire above the western woods. Down a long flight of steps the Lady went into a deep green hollow, through which ran murmuring the silver stream that issued from the fountain on the hill. At the bottom, upon a low pedestal carved like a branching tree, stood a basin of silver, wide and shallow, and beside it stood a silver ewer.
With water from the stream Galadriel filled the basin to the brim, and breathed on it, and when the water was still again she spoke. 'Here is the Mirror of Galadriel, ' she said. 'I have brought you here so that you may look in it, if you will.'

JRR Tolkien: The Lord of the Rings: The Fellowship of the Ring: Book II, Chapter 7: The Mirror of Galadriel