 In the series finale, Giles says that there is a Hellmouth "in  Cleveland". This is a reference to another throwaway line, in  the/spot Season 3 episode "The Wish": in an alternate reality where  Buffy never came to Sunnydale, Giles phones her watcher, and then  says, "Yes, I know there is a lot of demonic activity in  Cleveland.... There happens to be a Hellmouth in Sunnydale...."