Share 'What are some spiritual adventure novels?'

By these, I’m talking about works of fiction. Famous examples are books like The Celestine Prophecy and James Redfield’s works in general, and Diana Cooper’s trilogy of novels (The Silent Stones, The Codes of Power and The Web of Light). All three of the latter I would recommend reading, they are really absorbing.  Can anyone think of any others? I’m really in to this kind of story at the moment…