Mount Sunday is a hill in the Rangitata Valley near Erewhon on which Edoras, the capital of Rohan, was built for Peter Jackson's film adaptation of The Lord of the Rings. Though Peter Jackson found Mount Sunday to be a perfect location for Edoras, some still say that the hill was too small for portraying Edoras accurate to the books.[1]
It is very windy there, as shown in the first Edoras scenes of The Lord of the Rings: The Two Towers.