This is a longshot, and I am not sure I really started reading it or if it was a dream.
The story involved the main character(s) traveling town some river in another time/place/dimention. Maybe aliens were involved, maybe the book had a religious theme. I acquired the book from the same bookshelf where I found a bunch of Left Behind novels, so the religious connection could be there.
I think the main character(s) kept encountering new and different peoples/creatures during the trip.
I wish I had more to go on. I know I did not finish reading it, and i want to find out the title so I can read the rest. Thanks for any help!