The Niagra Falls were a location on Earth. The Tenth Doctor once recounted a tale of him going over them with a Chelonian. (COMIC: Silver Scream)
Behind the scenes
In an InnerSpace interview for series 10, Peter Capaldi commented that he hopes Doctor Who films at Niagra Falls. Capaldi feels it's a location he's not seen on film or television in a while, when it used to be quite popular.