In The Hills, The City is a perfect example of this. It's my favorite Barker story.It's hard to say where the line is between horror and fantasy sometimes. The main criterion to me is that for me to call it horror, it should be dark. There should be a dark sensibility to it. Barker always had that I feel. King too: The Dark Tower (well, the title alone gives that away) is fantasy with dark elements.
I personally sometimes prefer dark fantasy more than horror, because it feels richer to me. The thing about horror is that at a certain point you start to come across similar story elements over and over: ghosts, demons, vampires, werewolves, witches, the dead coming back. In dark fantasy you can have these elements, but do new things with them. And Barker has always been good at coming up with new subjects and ideas that feel fresh.