I THINK i read this book where there is a boy and a girl -possibly brother and sister- and someone is trying to do something to their idyllic town. Possibly this was a dream but my vague memories are too elaborate. There's a hill and i think they sleep on it at some point, and some old man who gardens vegetables, and there's a big (figurative) race with a round stone (i think) at the the end to stop whatever is happening. There may be elves or some magical creatures like that in it...Sorry this not at all specific so probably no-one will know anything but if anyone has any suggestions, please do say.
It's a long time since I read it, but Raymond Feist's "Faerie Tale" has a mound which a boy sleeps on and he is drawn into the realm of the Unseelie. I think his sister is trying to rescue him and there is something about the Great Hunt, though I can't remember a gardener or a stone. Anyway, it might be the book.