The Rauros-falls, also known as the Falls of Rauros or simply Rauros, were the great falls of River Anduin beneath Nen Hithoel, where the river fell from Emyn Muil to the wetland of Nindalf.
The Kings of Gondor had built the North Stair, a portage-way that bypassed the Falls.
At the breaking of the Fellowship of the Ring, Frodo and Sam paddled a boat from the west bank of the river to the east just above the falls and had to use all their strength to avoid being swept over the falls by the current. Shortly afterwards Boromir's body was placed in another boat by Aragorn, Legolas and Gimli who sent it over the Falls. Aragorn declared in the Song of Boromir that ever after the Tower of Guard would gaze "to Rauros, golden Rauros falls until the end of days".
But it apparently survived the fall; at any rate, soon afterwards it was seen by his brother Faramir upon the lower reaches of the Anduin in what felt to him like a dream yet from which there was no waking, and the two halves of Boromir's cloven horn were separately retrieved (neither by Faramir).