Do you know the title of this book?

I don't know why I just thought of this book, but now that I have, it's bugging me. Does it sound familar to anyone?

It's a fantasy. Two women go on a trip to a place that doesn't really exist. They have a guide book that really guides them, ie "don't go down that street", "don't answer the door." Turns out they were expected to arrive, they are supposed to do something that will save the, I don't know, kingdom for lack of a better word. In the end, one of the women stays and the other leaves, with a fake body so she can tell everyone that her friend died. I think they rode bikes for a good portion of their trip to the place.

Anyone???