I want to find a really good book to read on my vacation. Any ideas?

I am ready to go on my summer vacation in four weeks and I want a really good book to keep me occupied on the beach or at nights. I am searching for a book that will make me feel optimistic and broaden my horizons or something that will intrigue my mind, such as a mystery. But I want to avoid sad or crime stories… Have you read or heard something interesting from a friend?