Amon Sul:

The southernmost hill in the chain of the Weather Hills. The Road skirts along the edge of the hill. In the time of Elendil, there was a tower on the hill. The ruins were still there at the end of the Third Age of the Sun, when Frodo and the others were atacked by the Nazgûl. By that time, the place was known as Weathertop. The location was perfect as a look-out point, as from the top of the hill a person could see for leagues around.