E. L. Konigsburg
This one is just fun. Maybe you read it in elementary school, I didn't, but I should have. When Claudia, an unsatisfied 12-year-old, decides to run away from home and take her little brother Jamie, and his piggy-bank, along, she has a plan for everything. They pack their clothes in their instrument cases and head to the Metropolitan Museum of Art instead of school. While sneakily staying at the Museum, Claudia becomes entranced with the mystery behind a new sculpture and refuses to go home until they discover all they can about its origin.
Claudia and Jamie are easy to love, and their unique approach to running away from home piques intrigue and sparks imagination. All humans can relate to a child's dream of running away from home, and are able to rediscover that forgotten piece of childhood as they become involved in these very advanced, yet still juvenile schemes. From the Mixed-Up files of Mrs. Basil E. Frankweiler should go on everyone's library card queue.