For me it has to be J.R.R Tolkien's The Hobbit. Years ago I was given a box set of the Hobbit and the Lord of the Rings. I've read all of the books, but the one I come back to time and again is The Hobbit. I can't quite place my finger on exactly why I love that book. All I really know is that I do. Seeing the story line played out on the silver screen is a treat for me, but I think even after the movie sits on my shelf I will still crack open the pages of the novel and once again go on an adventure with Bilbo Baggins.
If you have a book that you can get lost in over and over let me know what it is. If you know why you love it then let me know that as well. I'm truly curious to hear what you truly love to read.